Why do people jailbreak or root their phones?

People seem to always want to jailbreak their iPhones or root their Android phones.For what reason.To get rid of the pre-installed bloatware apps on the phones.But,when they do these things their phones stop working properly.I hate the bloatware on my phone to,but i would rather deal witht hem and have a phone that works,rather than jailbreaking or rooting a phone and having it not work.