Hammer and Thumb...(40k application and rumination)

So, I was an artilleryman. It was our job to apply saturating fire from long range when called to do so. Sometimes this was going to be called on a target that was unaware and static, but as often as not it was going to be called on a target that was in motion. In order to pin that enemy down, friendly PBIs had to engage the enemy to keep them in place. We were the hammer, they were the thumb. Sometimes, the thumb got bloodied. It is a decision that has been made in warfare since the dawn of indirect artillery/aircraft bombing. It’s a decision not made lightly, but made of necessity. (note; though I was active duty during at least 2 military actions and 1 war, I was fortunate enough to never have to lay a quadrant/deflection or pull a lanyard on a live enemy, but we were trained to operate with these expectations).

In 40k, we have the viewpoint of gods. We see every aspect of the field, and the enemy, from on high…with little in the way of ‘fog’ (aside from dice uncertainties/human unpredictability) to disrupt our decisions. We DON’T have (even with vaunted IG arty) the ability to engage the enemy with no chance of reprisal. Our ranges are intentionally shortened to prevent this stand-off kind of engagement from being the totality of our gaming experience. Yet the concept of ‘Hammer and Thumb’ still applies.
In this case, it is the act of holding, baiting or manipulating an enemy into position in order to deliver a devastating strike.

As weird as it sounds, in our gaming example, the Thumb is as (or more) important than the hammer. In 40k, the thumb is often not expected to live but instead provide opportunities to apply the Hammer such that the sacrifice will further our cause far more than the loss of the unit costs us.
(I’m not listing Hammers and Thumbs, but application. Units such as THSS termies/Rampaging Carnifex Broods/IG Arty squadrons speak for themselves, as do all other ‘dexes heavy hitters).

Thumbs:
Units that cannot be ignored, cannot be simply swept off the table at a whim and can threaten on their own. Look at resilient scoring units, fast threatening units or outflanking/infiltrating units. Squad(ron)s of this nature can be used to influence disposition, deployment and movement of the enemy. Though not an exhaustive or restrictive list, I usually find these to be my best Thumbs.

-Resilient Scoring Units (ignore us at your peril). Mounted squads with large numbers/high toughness/solid saving throws. You cannot ignore them, they might grab an objective late game. You cannot just paste them, they have speed AND innate survivability. They will often survive your initial assault long enough to hold you down for the cavalry, or at least fall back/die in such a way as to leave you over-extended. If you have them, use them. IG have them, it’s called a platoon in chimeras. What they lack in T/Saves they make up for in spam. Marines have them, it’s called the Tactical Squad and rhino. Obviously there are others, but these are just indicative examples…find your parallels. These units can be held back and thrown out for late game grabbing, but applying a squad or two early creates a ‘must deal’ situation.
Threaten objectives or clog movement lanes. Block LOS with their cans. Pull assault elements forward with them as bait. Make a wall that cannot be side-stepped or ignored.

-Fast Threatening Units (you can’t guess where we’ll be). Tank killers, movement blockers and vehicles of all sorts. They may not be able to score, but they can contest. They don’t always have ‘major doom’ written all over them, but they will interfere with your opponent’s plans. Generally we’re looking for interference units here. Look for things that can threaten nearly all transports. Crack a can, and you slow your opposite number’s ability to respond, and keep his units at arm’s length for longer firepower attention. This is generally the true throw-away thumb. It does its job and you don’t care anymore. Great if it lives, but a valk dropped melta-vet squad cracking a Land Raider isn’t expected to last longer than it takes to expose the termies. It’s job is done. It has held the enemy baddy at bay and slowed it. Speeders, Piranha and such all perform the quick immobilize/expose/block role. TWC are generally considered hammers, and rightfully so. But they are GREAT thumbs! They usually survive their ‘sacrifice’, can threaten a greater portion of the battlefield, and serve a dual role.
Remember though, your Thumb (in this role) is quite literally a tool. Do not grow attached. Weigh interference vs your personal attachment to the unit. Use these units with a focus on blocking or holding units in place with little concern for their long term survival.

-Outflanking/Infiltrating units (you can’t guess where we’ll come from). These are Thumbs of a different sort. Units that serve this role are there to influence your opponent’s deployment/early moves. Drop Podded units, Mawlocs/Stealers and scouting elements are your friend. No matter how much your opponent may seem un-flustered by their appearance in your list, he WILL be considering where they will be when he deploys or takes his first moves. Anything that influences this gives you greater understanding of where he will be in the developing turns of the game. These units will give you greater control over what you do in your own development. These units serve their purpose early game, and what occurs after that is up to you and how you capitalize on their influence.
All of them have potential to shoehorn the enemy into less favorable deployment and less than optimal early movement. Of the Thumbs, these also have the potential for greater survival into the mid-game.
Use these units for early game manipulation, placing your opponent in the un-enviable position of deploying without regard for where they may pop, or let you have an easier time predicting where they will end up early.

Nearly all of these units require ‘spamming’ to be effective. A singleton of a unit will only make your opponent tweak a little. Doubling or tripling (or more in the case of scoring units) is necessary to influence your opponent’s deployment/responses. A single squad in a chimera does not a wall make. A single Land Speeder does not a true block make (etc, ad nauseum). You can’t ‘throw away’ something you cannot replace (either with a repeat unit, or a unit with similar functionality).
Always look toward manipulating your counterpart’s early game actions and you will have your first step toward victory.