IF you want to find out the optimum no of work processes there are two ways
1) Goto transaction sm50 and click CPU as shown in figure
or press ctrl+shift+f6 . You will see the cpu total times of the work processes . If you have WPs whose CPU time is very less (Say less than 0:20), you can decrease the number of WPS of that type . If the CPU time of certain type of work process is high, you may decide to increase their no.
2) Another method is to go for transaction Al12 then click all servers as shown
Then you will see the total no of requests for each work process. If all the dialog work process have large no of requests then you can add additional dia wps. If you have less dia wps with less requests , then you can decrease the no of dia wps.
This method is useful in deciding which operation mode to be used at a particular time.