Punch Through applies to enemies and allies only, but not surfaces of any kind, e.g. it cannot pass through a Shield Lancer's shield (possible bug due to conflict with bouncing mechanism).
Despite seeming to have only .6 at max rank, at rank 0 it can go through several grineer marines.
Update 13 gave Power Throw the ability to create explosions when hitting an object on its last bounce. This explosion will damage both enemies and yourself if you're near enough.
A maxed out Quick Return now synergizes well with Power Throw by creating explosions on the first object hit, since the throwing weapon returns to its owner soon after, thus counting as the last bounce.