Is it a good idea to use crutches for a bad sprain when you are out moving?

Yes. I recommend you use crutches until you can walk normally. The limp is a sign your injury needs additional healing time. Hobbling around unnecessarily stresses a joint that's trying to heal and you are essentially practicing that limp, which may make it harder to shed when you're healed. I recommend an evaluation by a specialist and physical therapy might be a good idea. Good luck.