That would be nice.
That don’t tell me if it can or not, just wan a simple straight answer, and how to do it, if possible.
Such a funny question 
Wherever plex is installed would need to be on to access it. How could you use something if its not on. If you have a NAS and install plex on the NAS then you don’t need a PC to access it so it could be off, but of course the NAS needs to be on.
A basic bit of research into what plex is would answer your question …
If you want to view your own media from your local storage - yes, the server must be on - the server can’t serve files to clients unless it’s on.
If you want to watch “Plex Movies and TV” - no, all that requires is an internet connection and a client that is able to access “Plex Movies and TV” - not all clients have been brought into the “Plex Movies and TV” world, but it won’t be long…
Help us help you by telling us what you’re using over there…
