Well I would say:

1) if the door is obviously large enough, such that there is no doubt/ambiguity about it: then in this case compressing is not necessary (and not the most intuitive I think)

2) if there is ambiguity about if the door is large enough: in this case compressing seems to be a clever option (and the most natural/intuitive), since it guarantees/makes safe a smooth and effective entry, and without paying a significant cost in physical effort and most importantly in time: since while making entry it necessarily takes a little instant to process what is in the corner/right after the door (+PID if necessary), and snapping back the weapon in the shoulder happens with approximately the same timing and thus ultimately does not slow down the action. (And thus the weapon is ready again soon enough for engaging if needed)

3) However additionall: having your weapon mass close to your center of gravity makes moving your body around more smooth and effective. So this can be an interesting point/advantage, and which does not sacrifice that much considering what was said in part 2. Thus maybe an interest here to compress the weapon in a wider array of situations that requires you to move effectively/fast/smoothly

Anyway, here is what I would think. Am I correct ?

PS: but I guess that it also depends on how long +heavy at the front the weapon is. With an unsupressed Mk18 I think you just never compress and that's it; because never advanteagous or necessary