It depends on the shot. Generally you want to keep your compositions as simple as possible and still sell the effect. Matching a keyed shot with the background can involve light wrap, matching grain, color grading, and a bunch of other things. I've had successful composites using Keylight that had as few as 2 layers and had some that had 10 or more. It all depends on the shot and the background. No one technique works all the time for every shot. Checking the channels is not as important as checking the shot playing back at full scale and full frame rate. Many times this is only possible if you do a test render. You cannot judge any effects or composite shot by looking at individual frames. You have to look at it with the footage playing back in real time, especially if you are trying to match noise or grain. In 20 + years of using After Effects almost every week I don't think I've ever just thrown in noise to try and match a shot. I've used all kinds of noise for other things, but I've never relied on just noise to match grain or video noise.
Thank you very much Sir, It is always good to here from you.
Also note, that the keying process itself sometimes accidentally introduces noise. So make sure to set KeyLight parameters properly to avoid that instead of removing or matching it with other effects.
I show an example for this in this tutorial (chapter 3 is about the keying with KeyLight)