General advice - Increase the number of work processes gradually:
1) Add x additional dialog work processes.
2) Do not stop the Sap system for a week - lets say.
3) Using sm50 you can observe if the x additional dialog work process
were used ( cpu time greater than zero).
It makes no sense to add work processes if nobody use them.
4) The ideal is a configuration in which at least one (but no more this is not a rule, please get the idea and not the numbers) work process is always free.
5) if necessary, repeat the above four step with the other kind of work processes , EXCEPT ENQUEUE WORK PROCESS.)