How important is it to crate your puppy when he has a broken front leg?

If your vet told you to keep him crated, than do your best to do so! The only time he should come out is when he is HIGHLY supervised by you or someone else. It is extremely important to let the leg set up in his cast (assuming he has one if the leg is broken) and if there is too much stress on the leg (such as having the pup walk on it) it wont heal right and if it does heal ok, it will take longer than a dog who had rested the leg because the stress on the break kept undoing all the work the body was doing trying to heal the leg.