It is a TERRIBLE idea. A rebuilt car has, at some point, been declared a total loss. Never believe those ads you see on Craigslist. "Oh it was barely bumped. It was a fender bender", etc. Insurance companies usually do not offer full coverage on them either.

Just a headache you don't need.

yes

… very, very bad, … unless you see a single part - one that you desperately need - and is more expensive, otherwise, than a purchase of a complete rebuilt vehicle with that part! Most cases true, … 

F.S.

If you decide you must buy one look to see if it has new tires. A lot of time rebuilt cars have serious tire wear issues due to bent frames and components. If it has new tires especially in the front this may be an attempt to cover up the wear/alignment problems. Cars like this are often not repairable.