there are many advantages to lapping, the biggest of which is that your scope will survive even the cheapest of rings without a scratch. i personally wouldnt say there are any true disadvantages to not lapping as 99% of the rings out there are not lapped and work just fine. i would say its like getting another option in a vehicle, it might help but its not really necessary to essential function. albeit i still lap all my rings only out of precaution. but of all my rifles i have only ever found that proprietary type rings like sako optilock, ruger's half moon dovetail and cz's lug + dovtail needed lapping but thats because ive found them to often have a lip on the rings edge. especially with rugers cast rings. so if you have access to tool steel and a lathe go ahead and make a set but otherwise you should be fine unless your rings have some obvious flaw.