* Theoretically, stuffing is preferable to rolling; it is easier, it may possibly perhaps maybe do less damage to the bag (more consistent compression, and it does not create wear spots. However, the crease-wear that occurs on tents and similar flat goods is less likely to occur with a sleeping bag because the creases are unlikely to occur in the same place very often. You probably would not be able to detect unusual wear after long use. That said, I stuff because it is easier.
* It is always better to avoid any unnecessary compression. The more (and longer) an insulation is compressed, the less it will recover and the longer it will take to recover whatever loft it has left. This is true regardless of the insulation.
* Compression sacks may overcompress the insulation. Use the largest sack compatible with your pack. The goal is to protect the bag, not to see how small you can make it. An odd historical factoid: Golf balls were originally made by pounding goose down into a leather sack. You can compress down into an amazingly small space. Whether you will get a warm night's sleep out of it afterward is another matter.
* Silicone impregnated nylon or polyester stuff sacks are easier on sleeping bags because they are slicker. Each handfull of sleeping bag slides in with less pulling and stress than with polyurethane coated sacks.
* The tried and true technique for stuffing a sleeping bag is to bunch the foot of the bag and cram it all the way to the bottom of the stuff sack. Then grab a handfull of bag just above the opening of the stuff sack and cram it all the way to the bottom, next to the foot. Repeat as necessary, stuffing each handfull as far down as possible and filling the soft places as you go. After a little practice, you will find the right amount of force to apply. Use the minimum necessary to do the job.
* More damage is probably done to sleeping bags through improper storage than through improper carrying. Be sure your bag is dry before you put it up after a trip and store it loosely in a well-ventilated area. I prefer to hang my bags, but nowadays some bags come with loose storage bags that are meant to be hung. That's OK, too.
* With good care, a good down bag will keep its performance for 15-20 years. I have one bag that is still in pretty good shape after 30 - although I have given some thought to replacing its down with higher loft stuff - just because I can.