Peeking over walls or around corners has a massively negative impact on gameplay by adding assymetric vision where one party can see the other while remaining 100% hidden. This emphasizes hiding and camping and disallows the use of several tactics. It also reduces the vision disadvantage aquired by using particular items (mostly jackets and backpacks).
It also imposes a massive handicap on the use of the first person option which in turn increases demand of servers limited to this view. On the other side many players like to see their character in third person at least from time to time for various purposes. Overall this results in a split of the community.
To solve the issue there should be something like the "Fog of War": People are able to use the third person view but non-static objects (players, loot, NPCs, some effects etc.) aren't visible outside the natural "first person" vision area.