Panning is very important, but must be used with caution. If you are planning on making your percussion very wide, then this leaves little room for leads and other instruments that are phased very wide to breathe. I look at stereo width the same as i look at EQ. Everything works best when given its own place in the stereo field. I also use stereo phasinf when i have 2 sounds that use up the same freqs. By making one sound a bit wider, it stops it clashing and leaves both sounds clearly audiable. I usually do it this way -

Kick and bass - dead center
Mid percussion - Near center
High percussion - Some elements panned wide
Ride - Dead center
Main lead or hook - Wide as hell
*Little high pitched glitches and beeps - Fully panned from left to right

*I usually put high pitched little snaps, only a few milisecs long to add extra width to the mix. Even though most people wont notice them, it makes the mix seam a lot more natural and polished...