Yeah man, I steer super clear of those youtubes.
The majority of my tech questions I just get on the [H]ardforums, for like 15 years. Its an enthusiast site and there is a ton of knowledge in there. Lots of helpful people. [H]ardocp recently stopped doing articles and reviews. But the forums are open for the forseeable future. And Kyle the owner, is still posting.
With fan cooling in a PC, you basically want intakes to be facing the hottest areas. And then exhaust to be somewhere opposite of that. Most cases are usually designed with one or two general ways to orient things for airflow.
Most PC fans are designed to push, not pull. So, if you have a GPU situated where its own fans are well inside the case: those fans are going to passively pull air which is already inside the case. And therefore, heated air. Probably air the GPU itself, heated. Even though there are vents only a few inches away, those fans are designed to put their force into pushing. Not pulling. By the time that air passively enters the vents and makes it to the GPU fans, its gonna be warmer than when it first came into the vents. And those GPU fans are still also just using air which is already in the case. Its kind of a circle. And GPU fans are relatively small, so they have to spin really fast, to push any reasonable amount of air. See: noisey.
So, you put case fans right against the vents, so that they push the air forcibly into the case. Straight at the GPU fans. This bathes the GPU area in that fresh air, which means the GPU fans are gonna get more of that to push into their heatsinks. This will also create more positive pressure to push old case air away from the GPU, towards the exhaust. So the GPU doesn’t just recycle that same warm air, in that circular cycle I mentioned.
ANNNNNND, since the GPU is now getting cooler air in this new positive cycle: You can probably run the GPU fans at a lower speed to still net good temps. Thus, bringing down your noise level. Because case fans are big and good ones don’t need to spin fast and loud, to push in a reasonable amount of air. So your gross volume is lower.
*don’t be afraid to experiment. With cases, intake is generally better than exhaust. Especially small cases. That hot air will find some way out. But it can be tough to get cool air into the right places. I only worry about an active exhaust, if there is a place for it which make sense, totally opposite of the places I want to intake. Otherwise, powersupplies are generally the main exhaust. And those things are designed to run hot, so its fine.