Some people prefer one or the other, sometimes both. As far as shortening the life of your atomizer, I don't know. But, just like Houdini stated, I'd worry more about your battery if you're using an automatic (but if you have a manual, ignore this). I actually gummed up one of my auto-batts on my M401 on accident due to juice leaking into the battery sensory hole. It charges like normal, just doesn't work :[
Personally, I like using a cart when I'm driving or out with friends, since carrying around all my equipment is a bit tedious. But, at home, dripping provides a better taste and massive amounts of vaper for my 510.
Also, depending on your model, if you have an exposed atomizer (like the M4 series), dripping is viable, but alot of people are raving about dipping rather. You can find various threads for these methods.