Consequences of splitting to multiple Porjects and Solutions

Can someone point me to any training material discussing the reasons for having solutions AND projects?

I'm brand new at this and I don't yet know if there are any consequences or benefits to keeping all BPM processes in one all-encompassing solution, split by (for instance) Department projects verses one all-encompassing solution split by process projects (each containing a single process, or a physically piece-wise process) verses multiple solutions by Department ....

Are such training materials available? If not, can anyone suggest workable structures?

Thanks,

Jason