Question: what makes a type ia supernovae good standard candle and useful for finding distances?
Answer: At larger distances, we need brighter standard candles. Type Ia supernovae are superb standard candles. They are all basically the same (if you've seen one carbon-oxygen white dwarf explode, you've seen them all!) Thus, all Type Ia supernovae have about the same luminosity: L = 4 billion Lsun.