Which Locations Should Not be added in windows search indexing?

I am afraid that all location should not be added in windows search indexing Which Locations Should Not be added in windows search indexing? because if we added whole c:\ drive in locations, indexed database collected by indexing itself also added in index database like self database indexing. is that true ? or affect on indexing? can anyone guide about that indexing not corrupt or damage through long locations added to indexing.? hope there are some rules for that. Regards, Chirag Raval.