When the Plex Media Server has an update, there are currently 2 options Dismiss or Download. I often find I then copy and paste the version number into google with the works Plex Update to see what the features are.
I think with every update, there should be a third option of Whats New which opens up a tab with the change log. This would allow for the ability to see what is new before deciding if you need to update or postpone. I typically will ensure I update timely for issues that impact (or may impact) me.