on the street it will tear stuff up- a friend of mine had a jeep with a locked up rear posi unit- when turning corners it didnt just 'squeal the tires', it would kinda chirp,chirp,chirp, violently, tugging at the steering as it turned corners...large tires probably aggravated it...would think twice about it on the street...in the wet you could spin out very easily.
limited slip can have similar problems, but not nearly as bad. I remember years back, hotrod had an article on "$1.98 posi"...i think they just shimmed spiders a bit snug in 9" ford, got carrier drag similar to that of limited slip. I'll see if I can find the article...
Confidence: that feeling you have just before you realize the mess you've gotten yourself into...