Compression is talked about a lot in mixing music. With DAWs bringing in a lot more entrepreneurial music production there is a significant point that is often overlooked.
Compression is, in a sense increasing RMS. What this means is a flattening of the sounds so the overall volume can be raised.
When you are creating music in a DAW, using pre sampled audio, these before they have gotten onto your track have most likely been treated/compressed/equalized. This is not to say you cannot get different effects for doing more of the same, but is a word of recognition when you are mixing and wonder why that compression effect is not having the effect you think it should is to consider the true value of that tool is for live recordings and even live performances. Go light on compression in audio sample situations.