Reducing the weight of the slide allows you to run lighter loads and springs. It's no different than running a lightweight BCG with a different spring/buffer combo in an AR.
And just like running lightweight components in an AR, my concern with slide cuts are with reliably cycling factory ammo in a defensive ammo. I wouldn't be too concerned with dirt boogering up a pistol. The M9 has the most skeletonized slide I can imagine and it works fine.