JTUK, a question for you...
Say you want your notes to have more attack on a song, but you dont want the output to be louder.
Now on the next track in the set list you want the attack to be less overt, but you want to be just as loud as before.
Using just your hands, how do you do that??? If you play with more attakck you will get more volume, more input means more output. You could try turning the volume on the bass down a bit and playing harder but thats not a very precise solution.
For me and all other compressor users who know how to set up a fully featured compressor, thats as simple as using a compressor to change the ratio of transient to sustain in the envelope of every note played at the required volume. Done using a compressor, because thats what the tool is for. Slow attack, medium release, 3:1 ratio, threshold set so you get the right tonality, make up gain to bring the level back. Easy. It wont effect my dynamics at all, since its not going to be squashing anything very hard, and the natural attack of the note isnt being compressed.
Some sounds you can't actually recreate without very liberal use of compression (Sledgehammer for instance) other times you can get a sound that better suits your requirements by using a compressor. Its not relying on the device to 'fix' some deficiancy, its all about getting the sound you want with tools that are available. Thats all - for me any way