If you don't have the time to go catch small animals, or lack space or even a freezer.
Dry food will see you right, of course, baby chicks, small birds etc etc, is probably the best diet.
Anything meat based, just stay away from bread and milk sobs....
I prefer the dry food, as someone said it keeps the number of flies down during summer time, plus its easily stored. The ferrets eat it just as keen as small birds and their condition is great.
For my situation i cant fault the dried food, i also give them some liver or an egg every now and then.