Conceptually they're the same.
I never did any tournaments.
Injuries can happen at practice, but it's extremely rare. A lot less lightly than in many other sports IMO.
Sore, exhausted, some slight bruising. Offcourse you might end up sparring with an idiot trying to prove himself/herself, but the coach will usually watch out for that and let them know before you have to. Going at it to hard is the same playing the drums fast and sloppy. Most sparring we did we called out 50-80% intensity. Going all out was a minute or two here and there.