They only NEED to be trimmed if they are super long and curling under and affecting his mobility, but if he's scratching you when you handle him, you can trim them for your own comfort. If he has natural rocks or slate tile in his viv, then that should do the job of keeping them filed down okay on its own, but if not, it's totally fine for you to give them a trim. Unless your beardie is very placid and doesn't mind being messed about with, the easiest time is after he's asleep...cover his head with a cloth to keep the light off his face, and he should let you trim them without too much fuss.