Excellent reply, the main differnces are that a turbo needs a certain amount of exhaust speed to drive the turbine fast enough to generate boost, the supercharger does not as it is always ready and does not need spool up time.
I think that turbos are newer ?, as I know old racing "BLOWER BENTLEYS" were kicking the germans bums years ago in racing, these had superchargers, as did spitfires, two stage if I am right ?
Dump valves are there to help prolong the life of turbos due to reasons mentioned,ie to elliminate as far as possible compressor stall, the fact that they are fitted as standard on a most turbos installs must mean they do something or manufacturers would not waste their time with them.
Anyone older than me care to tell me I got it all wrong, probably.
tabetha