Why/When should a dog wear a muzzle (not as a punishment tho)?

That’s what I worry about in my pup. He’s teething now AND he’s a Belgian Malinois which is a super mouthy breed. I’m just afraid he won’t grow out of it and I’ll have to muzzle train, he can be quite reactive too. Obviously I’m training and stuff, but I keep seeing it be really common for German Shepards, Belgian Malinois etc to be muzzle trained due to that reactiveness.