In bladder stretching why would some people need augmentation and others just need hydrodistention? Which is more effective?

Depends on severity. Bladder distention is the most common treatment for interstitial cystitis and is sometimes, but not always, effective. It involves filling and distending the bladder with fluid while under anesthesia. Bladder augmentation is a surgical procedure and is used only in the most severe cases. Research and discuss augmentation thoroughly before considering it. Medication is also effective sometimes.