Default Why do people need write protection disabled when they boot into system?

From all I am reading, Android disables write protection when you boot into recovery and any changes that you make in recovery stick when you boot into system. And if you have root access, you can make changes to system in recovery.

So what advantages are there to having write protection disabled when you boot into system? Why can't you make any changes you want while in recovery? Isn't that safer anyhow? Do some apps need write protection disabled to run?