What are the benefits of a Property Manager?

[Bob Lowry]

Would like to get some feedback on the pros and cons of using a property manager.  I have seen some that offer online portals for tenants, vendors and owners and therefore keep all communication and financials tracked.  I also can see the benefit in helping to find tenants and manage the late night calls, financials, and general headaches.  Wanted to hear what owners feel might be pain that a property manager can solve.  Also at what expense (fixed rate, %of rent, etc.)?