Honestly, I do not know the effect of increasing or decreasing the number of work processes.
For one application pool, how many workflows should be allowed to run?
I follow and I look for it in the documentation so that you do not run more workflows and then twice as many processor cores.
You should also be aware that increasing workflows creates a web garden. All workflows have their own copy of the application state, session state in the process, caches, and static data.