Disk Cleanup/ Defrag Individual Stations

I just got a job in an office with an internal server/network of 6 computers. I have never worked in an office environment with its own network before, and I’m not sure what’s good maintenance on individual stations…

I was going to do a disk cleanup/defrag on my individual station, but the owner of the business wants me to find out if that would affect all the stations on the network, or just my own…I haven’t a clue – anybody got any advice???