This is like asking: what's the difference between a horse?
In other words there is no possible right answer. Getting it right at tracking is the goal, as long as you know what it is you will be wanting at mixdown. Squashing the snot out of a signal is good if you need power, weight and healthy RMS. Letting a track breath is good if you need dynamics. It depends completely on the genre, the tune, the source, the player, the drugs......
Compressing everything is usually not a good idea. Compessing yoursellf into a corner that you can't get out of at mixdown sucks. Pushing the faders up and being exited about the song is good.
Some sounds can withstand abuse better that others. Bass likes compression. So do room mics. A well compressed vocal sound can take a good performance over the top. I've been getting into double compression. Letting two different boxes do different things. i.e. Distressor into an eq into a dbx 160. Let the Distressor catch the runaway transients with a really quick attack, just taking a db or two off the top, then letting the 160 do its slow squish thing after the eq. Lots of room to juggle the tone.....