In an emergency, the handbrake is very unlikely to help. It is likely to put you in a slip. Especially in a car with ABS and traction control, where normal brakes are far more effective.

The only emergency it is useful for is when you really have to pull a 180 right now and tight, as the automated systems do not expect this situation and will relax the brakes while you're deliberately trying to spin. I wouldn't trust even an above average drive with pulling that off - it's not being practiced. Usually it would be a desperation move when there's no space and a head on collision is likely.