That’s called cache buster which is absolutely needed when you are using the default page rule-based caching system. If you enable the worker mode inside the plugin settings page, you will see that the cache buster will go away.
Also do note that the cache buster is only visible to the logged-in users and not non-logged-in normal users.
All of these things are clearly mentioned in the plugin description section. Instead of asking things that are already mentioned, please read the plugin description section thoroughly and also watch the YouTube video embedded there. Also checkout the FAQ tabs inside the plugin settings page.
The answer to most of your questions is mentioned there.