You basically have 5 years of the right to live and work - unrestricted - in the UK. The main condition is that you can't have recourse to public funds - which means a range of services designed for those on low income:
Public funds You still get things like free medical (NHS).
The benefits more generally of the Ancestory Visa are that you don't have to reapply, don't have to worry about points scoring, or being in certain professions. You don't have to be employed continuously. And it's a fairly easy (almost guaranteed) path to citizenship.