Typically kicks. snares and hats are mono and should be recorded as such. Recording a mono source in stereo buys you, well... pretty much the same affect as moving the fader up a few centimeters (i.e. nothing). However some sounds are deliberately stereo. These sounds may have an effect applied such as a delay, hall, etc. USE YOUR EARS. Try switching your monitors from stereo to mono (if you have this capability) while auditioning your sound. The stereo field will disappear and be heard dead center. If the source is mono to begin with you will hear no change.
Hope this helps,
ddot
