I had to rush home today because one of our admins had changed something on the website & it took off an iframe/article viewer I had on there with was custom code only I knew & also changed styling of our homepage blog boxxes.

 Had there been a revision history button for each page they could have just clicked revert to the last version before they had edited & then it could be fixed instantly. 

 This also could be a great way to troubleshoot problems & changes for support. 

Google uses this with their free google sites which i have a couple websites with & it is VERY helpful for going back in history if you are not sure what was changed.