Why parallel compression?

After reading this about parallel compression, I'm wondering how is it different from simple compression with makeup gain on the compressor's output?

With parallel compression, you can mix the compressed (wet) and the uncompressed (dry) signal. They are heard at the same time. Tha makeup gain in compressors is for bringing back the lost volume that is caused by compression itself. This means you only hear the compressed signal.

This article gives a very in depth view on the subject.

Unaltered dynamics can mix very well with compressed dynamics. Just opening up the attack and shortening the release doesn't do quite the same trick as mixing in the dry signal. I like comps like Reacomp with wet and dry so you don't have to buss it out. I VERY rarely use compression in any other way than parallel.

Well I've been mainly trying to do it to drums but I didn't realise how much actual GR you should go for. The drums got thicker but not punchier. I'll certainly try it with a much lower threshold and up the ratio