A desktop PC cannot store all of the files that may be needed in your area of work.  It needs enough memory for all its software applications as well as actual data files created by the user.  A desktop PC also needs space for archiving and caching.A server, which has all sorts of storage and file capacity, is useless without a PC interface to reall all the information.  It merely stores files, which are accessible anytime for all users pull as they need it.  A server must be active for 24 hours so that its public files are always available and so that it can consistently maintain the network.