computers necessary

are the blitz computers necessaryor are they just a different way to read certain stuff about the car. i know different computers for cars have different uses.

Necessary for what? What exactly are trying to do?

are the chips just for reading temp speed hp etc. or do they help gain hp?

A chip can change the air/fuel ratios, ignition timing, shift retard, red line, and some other stuff. With no other modifications you may see some power, but not a whole lot. With bolt ons such as intakes, headers, and exhaust sytems you will see a little more. Changing the computer or adding a chip becomes a significant advantage if you've done head work, cams, internals, or forced induction. A custom chip produced from a dyno tune is the best way to go.