Full Precision UV's performance?

How much of a performance hit is it to use full precision UV’s?

Because it is really annoying that without this option on, all my props have some weird normal map artifacts in UE4 compared to other renderers like Marmoset, for example.

I’d imagine there’s a reason why this option is off by default. Optimization reason, of course.
Yeah, I’ve googled that without it the engine uses 16 bit UV’s as opposed to full 32 bit. But it’s unclear to me if it’s something that would drastically affect performance of the scene.