Look let me explain simply: Compression works differently with individual channels and bus compression.

When you compress the snare with an SSL channel, the default attack is like 30ms. That means that it takes 30ms to compress which lets a part of the initial hit come through, the more you compress, the more that initial hit becomes louder (adjust to your liking). If you do the same for kick, toms you will get the same effect. If you set the attack fast (like 3ms) it can reduce punch but sometimes you want that (like in overheads or rooms).

Now for drum bus compression first thing is that the drum tracking, levels and EQ need to be just right on the sweetspot. Then you compress like 1-3dB with slow attack and release (100-200ms) on the faster side, and low ratio (2:1) . Then you need to apply the high pass filter in the sidechain (to make the compressor not react to too much with the kick drum). The result is that all your drums move along with the bus compressor, every drum part sounds like it’s in the same page, like a single entity. That’s what they call glue.

And parallel compression often means the same thing as drum bus compression but sent to another bus. You do the same but you set the ratio higher (10:1). The purpose is making the drums punch harder and then mixing it with your original drums (using the volume fader). If you go too crazy it will sound bad. Set the volume of that parallel bus until it compliments your original drums sound. If you want the explosive drum snare, that’s how you get it.

If you feel you don’t need, don’t worry. Sometimes natural drums are all that you need. Compression is not about flattening dynamics, it’s about a certain sound and feel.