some airports will allow you and help you to descend imc and then resume your own navigation before being on final approach.
What do you mean?
At an airport with a procedure you could fly the procedure and once established VMC ask to terminate the procedure and continue to make a visual approach or break off the approach completely and depart en route. With the consent of AT I see no reason why you should not do so at any point in the procedure. For example if you arrive in the hold in IMC at 3,000 and descend in the hold to 2,000 at which point you become visual and request to break off the procedure with consent I do not see an issue. This might for example prove a useful means of making a let down whilst ensuring adequate terrain clearance and in theory seperation from en route traffic.
That aside I dont see how else AT could "allow or help you" with a descent from to IMC to VMC - for example if you were to arrive in the overhead of an airport without a procedure in IMC and descend in their overhead they are not in a position to "guarantee" any terrain seperation or seperation from other traffic any more or less than en route.
It amy be true that they will have a better idea what traffic there is below the cloudbase than you might en route (assuming you cant receive a RIS and non transpoding en route traffic beside) and it may also be true that you know very specifically where you are and therefore what terrain implications exist but you are now involved in a "home made" letdown with all the risk involved in doing so.