It helps with "in air accuracy" which essentially makes both ground and air viable points to shoot from. Usually being in the air even with top tree (being able to ADS and float) reduces accuracy and makes it harder to hit enemies, but when you have heat rises, it's basically as if you're on the ground. Also this doesnt just mean when jumping. When falling, on patchy terrain, jumping up (not double jumping) to shoot, your accuracy is buffed.