well... both in a way.
in powerlifting, the aim is to lift the most weight.
so you do whatever you can with in the rules to get in to a position to lift the most weight.
eg. Using a close grip bench with your elbows flared, back flat, lowering the bar to the middle of your chest will probably built a bigger chest.
But using a wider grip, bringing the elbows in, arching your back, and pumping your chest up and lowering the bar to your lower chest (which will be the highest point when your back is arched) will probably allow you to lift 1.5 times more weight due to recruiting the triceps and delts more, your lats some, and with the hands wider and chest up, the range of motion is also shorter.
having said that, lifting heaver weights leads to more strength and size.
In powerlifting, as I said, the aim is to lift the most weight.. so powerlifters do it to lift more weight rather than to become chesty brahs.
you'll see it in squats and deadlifts too.
squatting with a wider stance gives you more power once you get used to it.
squatting with a narrow stance means the range of motion required to get your hips below parallel is longer and doesn't use the hamstrings much.
bet you get massive quads.
wide squatters get to use quads, hips and hamstrings. end up lifting more weight.
Deadlift - some lift conventional (feet close and hands outside of feet), some lift sumo (feet wide out and hands inside right to the edge of the knurling)
reduces the range of motion, but need different muscles used.