I particularly don't want to be drinking sugar during my workout, then again post workout. I would prefer insulin levels to spike once w/ my post workout shake and that's it. I drink water during the workout, then after I have the dextrose/whey shake.
If you want to bulk and are worried about muscle glycogen, all you have to do is eat carbs before a workout. I'm sure when bulking you have enough carbs to last you the workout and then some. You're not going to be catabolic that fast.
If you want to burn fat, you'd restrict carbs. I wouldn't particularly take them w/ my workout, I prefer after. But I would make sure I take in enough before I workout to last me the workout and then replenish it w/ the shake. You want your metabolism to be raised for several hours, that's where the fat burning you want. Raised metabolism and restricted calories.