On the fittings, the type that slide in and get 'cinched' down, a 1/2" pipe no longer is a 1/2" pipe because every fitting becomes a choke point. That restricted flow may or may not be an issue depending on the end use of that run.
The fitting that expands the pex, is slid in, then the ring is 'crimped' on, the fitting is not a restriction. 1/2" stays 1/2" of flow.
