Question: Sometimes I make whipped cream in my ISI cream whipper and it comes out beautifully fluffy and smooth, and other times when I dispense it, the cream looks "ragged" for lack of a better description. Any ideas what factor accounts for the difference?

Answer: 
I was taught how to whip cream with a handheld mixer and there are a few things to consider

Is the whipped cream being over whipped? When you beat it too hard with a handheld it starts to form ragged peaks

Is the cannister almost empty? Gas charged cannisters often 'sputter' a little bit when over-charged or almost empty.
Whilst resolve whipped cream dispenser is important, it is more important to give the liquid time to dissolve the nitrous oxide into the fatty components. If it doesn't have time to dissolve, it will force them liquid out, bit it won't expand evenly as it leaves the nozzle.