they can inhibit if they are really packed full, then there's not much circulation through the bag. since the hops will swell up in the boil don't pack the bags anything near full. if they are compressed or plug whole hops they will expand like a dry sponge, if they are loose whole hops they will soak up wort and expand a little. you want to be able to feel them flopping around in the bag once they are completely hydrated, not clumped together like a sausage. if in doubt use more bags.
i then let the bags drain at least 10 minutes above the wort after cooling and during knockout, before giving them a firm but gentle squeeze between two well sanitized steel spoons. they will still hold onto a lot of wort, that's just how greedy they are, you can incorporate the wort lost to hops into your future recipes.