I bet he uses CellTech for the same reason as everyone else.... Its common knowledge that if you "stack" Celltech and NitroTech, you can lose 157lbs of pure fat, and gain back 215lbs of hard, ripped muscle in only eight weeks, allowing you to pick up girls left and right, and become an IFBB pro all at the same time!!!!
Ok well, heres some advice on supplements for ya.. and why to bulk and cut!
First off, bulking is good because it allows you to eat like a fatass and write it off to The Cause. Seriously though, it allows more calories, carbs, etc into your body, and helps build muscle. Basically, eat a tonne and lift like a demon when you bulk. Downside is that you also add some fat...
Cutting is just the opposite, you cut to get rid of the fat you gained while bulking. Eat below maintenance, at or under 100g carbs/day and do lots of cardio, don't let up on your lifting intensity though.
For supplements when bulking, you want to use things like creatine (and not NitroTech, its overpriced, get yourself some good 'ol ProLab creatine, cheaper and works better) maybe some ZMA and a tonne of whey protein (I like optimum and prolab myself). Never take a thermogenic "fat burner" while you're using creatine, it defeats the purpose.... Creatine makes you retain water, and ECA makes you lose it...
For cutting, lose the creatine and ZMA, and switch to a thermogenic (no need to buy xenadrine of hydroxycut or anything, just use an ECA stack). Also, keep the whey protein in your routine. Do lots of cardio