Monitor changes settings

Can someone explain to me the difference between the settings to monitor Redirections vs. Modified Posts?

I’m very confused about this. On my system it was set to monitor Modified Posts but the redirect function wasn’t picking up manual changes to slugs on posts, so I changed it to monitor Redirections instead. Then it did work. But when I came back to the Options page, it shows the setting as still being “Monitor Posts” — so I’m very confused because I can’t even figure out if I made a change and whether that change worked.

https://ww.wp.xz.cn/plugins/redirection/