“less weight (as less material…)”
Not usually – more seatpost usually makes up for any difference (at least within a few grammes.
Anyway, as above, it’s just a more mtb looking frame with a smaller seat tube for the same length effective top tube. Giant pioneered it with the TCR and the truth is that the real reason was financial – with compact frames, Giant could get away with offering three sizes only and then using a range of stems and seatposts to get the fit right.
Benefits? they’re arguably more aero (more open around the rider’s knees which supposedly allows better air flow, slightly stiffer (smaller triangles) and probably the biggest one, a longer seatpost means more flex and therefore more comfort.
There’s no conclusive evidence that compact or normal (though few road bikes actually have completely horizontal top tubes now) is actually better so go for whichever you prefer the look/ride of.