I have a 3 or 4 with cuts, and several very similar pistols without them.
The argument for them on non comp guns is that by lowering the reciprocating mass of the slide, the muzzle flip portion of the recoil is reduced.
From shooting a bunch of basically G19 guns with a variety of slides, often on a timer, I would say that that effect is very minor, at best. Frame stippling and/or undercuts, support hand thumb placement and pressure, Optic being used, and weight of ammo all seem to have more effect on "muzzle flip" in my hands.
I have used a bunch of ported slides in run and gun events, Tactical games, and just training in mud, sand, and dust and have not had an issue with dirt/crap ingress. I think that is an old wives tail until you get to the "SCUBA insertion in a swamp" level of tactical.
So from my experience, they are pretty much aesthetic. If a slide I want has ports, I won't avoid it, but I don't seek them out either.
If you want to reduce muzzle flip on your CC carry gun and do something that measurably reduces splits Ports/comps or increasing frame grip (stippling or something like Talon grips) will have be money much better spent.
Slides I've used to form this opinion: