There is of course another reason; they're good, if cooked properly. So how do you rotisserie cook a chicken properly? First of all, remember that rotisserie cooking is a form of roasting. To roast something simply means putting it in the oven uncovered. Putting a bird on the grill with the lid down is roasting. What the rotisserie adds is even cooking. Because the bird is constantly in a state of being turned it will cook more evenly and the turning keeps juices moving and not dripping. A rotisserie chicken will be moister than one simply roasted.
Presumably the final reason for the popularity of rotisserie, or roast chicken is the fat content. By placing chicken on a rotisserie spit, where fat can drain away and not in a fryer full of oil, you see a drastic reduction in fat.
The first step to rotisserie cooking a chicken is having some kind of rotisserie and knowing how to use it. This is where that user manual comes in handy. Once you have the basics of how to use your particular piece of rotisserie equipment for your particular grill, it's time to get the chicken. It's best to start with a fresh, not frozen whole chicken. It really does make a difference.
The next thing to consider is the seasoning. Marinades, dry rubs and bastes will all work well with rotisserie chicken. Traditionally we think of basting meat on the spit, but that can lead to burning and requires more attention. Of course you may still want to baste during cooking to keep the bird moist, but a good marinade will do more towards a juicy bird that applying sauces while cooking. When applying marinades or rubs to your chicken do your best to get it under the skin and to the meat. Coating the skin will help make the skin tasty but won't do a lot for the meat underneath.
For the specifics of grilling your chicken on the rotisserie see my article on Rotisserie Chicken - Step by Step.
