The IMC
In brief, it allows me as a PPL holder to fly in cloud in all classes of airspace except class A. So here in the UK I can fly from my home base, near London and fly to any of the major airfields around the UK (except London Heathrow) and fly in cloud to get there and fly an IAP when I get there.
It does not allow flight in IMC in the airways. However it is possible to get around the UK outside class A.
Its fantastic and allows me to get all over the UK with a degree of certainty. I use it as a pseudo IR. i don't go along with the "to get you out of trouble" school of thought as you have to be current. I fly an IAP at least once a week so I feel current.