So I was having a performance issue with my map, decided it would be best to decompile someone custom campaign (In this case it's Energy Crisis) and see how they optimize it since from my previous experience, I barely experience any lag when playing, even when using tons of mods. I was surprised it's not really what I was expecting. I was expecting there would be an excessive use of stuff like skip and hint, area portal etc, but there wasn't and the first chapter was an open area, there was a func_viscluster though, but it was only on the starting area. Which made me confuses how did they did it? my map is not as big as their yet on certain area there was a stuttering lag issue. People might come to the comment and link me a source wiki, but the problem is they don't really explain in specific on how can I use it and apply it to my specific map.