a good dj knows when to put in tricks and when to let the track play
weather it be beat juggling or fader cuts, you have to do it with the right tracks at the right time. usually when you have 2 tracks mixing that are rather loopy and not progressing, or throw in a trick like a bar right before a breakdown to mix out or soemthing
but like i said, a good dj just knows when to do the trick and when to leave it alone. some guys do it every friggen mix and it can get on my nerves but then again i do that sometimes when im playing to a crowd of 10 or 20 just to be a showoff...