Pipe threads that are tapered seal themselves so no pipe SEALER is required on them.
However, pipe lubricant , such as teflon, is required to achieve the recommended torque to seal the pipe. Teflon and other thread lubricants will not seal but will allow proper torque compared to bare threads.
A sealer would be used in straight threads, such as header bolts open to a water jacket, that have no taper and require a sealant to keep them from leaking.
