Impulse wrote:What does the keyword Infantry have to do with it?
That's an excellent question, and my answer is: this is a huge thing to bear in mind when evaluating or comparing different units.
For example, I was comparing once the "Inceptor Squad" from the Space marines with our Crisis suits, which have a very similar profile and role (Deep Strike, T5, a lot of close range dakka, Fly). There is a lot to discuss here, but one of the keys aspects is that you can drop those guys inside some ruins, or in a forest's limit, and be saving at 2+ thanks to the "Infantry" keyword, while with your Crisis you are not gona get cover almost ever (except with weird walls or oddly shaped buildings). This is huge. Why? because the space marine player can drop those guys hidding from the big guns of his enemy, while not caring about the saturation kind of firepower (lasguns, bolters, pulse weapons). Your Crisis teams will fall in a place to kill its target (vehicles? TEQ?), but if your opponent happens to have 30 guardsman with nothing else to do that offer 120 shoots at ya, he will make 6.667 wounds to them (not counting drones, that's not the point) with only 120 points (+ officers) worth of guys. If you are in cover, those shots are dealing you 3.33 wounds, and that's only for having that keyword.
TLDR: It gives you A LOT of tactical flexibility in where to put your guys, because they will have a lot of easy covers that allow them to still do their job. Specially important if the unit has some kind of deployment shenanigan going on (infiltrator, Deepstrike...)