It is a good idea to use the flush every once in a while. It helps to clean deposits from areas where there is not alot of oil movement.
Just follow the directions on the can and you'll be fine.
If you do get a leak its probably becasue the seal or gasket was already worn enough to casue a leak, but it was sealed by a biuld up of gunk on the inside of the engine that was washed away by the cleaner.
