They relieve the pressure in the sump, therefore there will be less pressure in the head as well. Less pressure in the sump makes the oil drains work more efficiently. I have 2 lines (with no valve) going from the sump to the catch can and they never have given my oil a path to leave my engine.
Realistically my GTR is almost worst case scenario for oil problems, it's quick around a track (g-forces), cops a lot of boost and decent power, has no head restrictors plus runs slightly higher than normal oil pressure. I had severe oil control issues and the only thing that helped was vent from sump to catch can. Not only did it help but it 100% solved all my issues so in my opinion you're nuts for not liking the idea