Making the slide lighter means less mass, so less inertia, so that with the same amount of "push" it moves sooner, and faster.
and, while this can increase reliability with light loads, it can, if taken too far, reduce the gun's service life with standard or heavy loads.
Semi auto slides are a balancing act between mass and forces in both directions. Go too far and you have to do something to regain the balance.
Cut holes in the slide, reduce to a bare skeleton and you will need to increase the recoil spring power to compensate, or the gun will batter itself.
What is the tipping point? Engineers get PAID to figure that out. Mechanically, almost anything can be done to achieve balance, BUT one has to stay within that is both practical, and what appeals to the market.
A pistol with a skeleton light weight slide that needs a 75lb spring is not going to sell,
THere is another point, holes in the slide (or an "open" syle action) that "let dirt in"... also let dirt OUT!
In theory this should balance, but in the real world, sometimes, it doesn't.