One main fear with feeding live, is that the rodent will injure the snake.
Second, that it may be cruel to the prey.
Third, that they snake may refuse FT if all they've been offered is live.
I feed both, live and dead. Certain situations I chose to feed live.
Whenever I feed live, I watch to make sure the snake grabs the prey and starts eating before I close up the container/room/leave. This way you can watch and make sure that the prey doesn't attack the snake, and that the snake is hungry and wanting to eat. You don't want to leave live prey in "unsupervised" on the chance that the snake doesn't eat it and it decides to nibble on the snake instead.
Personally, I see no harm feeding live, if done in a responsible manner.
FT is alot more convenient for most and is safer for the snake ( dead things don't bite), but if that is not an option for you.....just make sure your snake eats before leaving them.