The biggest benefit of running a lighter spring is that when the gun returns to battery (the slide closes) the heavier the spring the harder the gun slams shut and pushes the nose of the gun down. When I ran 1911s I played with springs a lot. My favorite limited gun spring was a 9lb ISMI. I loved the way that spring felt but I could never get it to run reliably. Your recoil spring doesn’t just close the slide but it is responsible for feeding the next round into the gun. I found that the lightest spring I could run in my 1911s and still have good reliability was an ISMI 12.5lb spring. I admit the 9lb did feel better but if the gun was not perfectly clean or anything in it was just a little bit off it would jam and that was unacceptable to me. Now when we look at a striker fired gun we have an additional function that the recoil spring is responsible for and that is keeping the gun locked in battery (keeping the slide from opening when you pull the trigger). In a striker fired gun (M&P, Glock, XD, Ect) you have two springs working against each other. While the recoil spring is trying to keep the slide closed you have the striker spring pushing in the opposite direction trying to open the gun. This means that the recoil spring is responsible for closing the slide and keeping it closed, feeding the next round into the chamber, and overcoming the striker spring. I value reliability above just about anything else so I come down on the side of running a little heavier spring for the reasons I listed. If you are going to run a lighter spring you should really up your maintenance schedule because you are running on the edge of reliability. And if you are going to run a spring lighter then 13lb you really need to lighten your striker spring. Here lies the second problem for me. A striker fired gun totally relies on spring pressure to ignite the primer. There is no hammer momentum like you have in a 1911, CZ, Ect. This is why all the Glock guys say that if you run the reduced power striker spring you have to run Federal primers. This is because you have lowered your ignition reliably so they start using the softest/easiest to ignite primers. That alone should tell you how close to the edge you are concerning reliability. But in the end you have to decide what works best for you. While the lighter springs do feel better I do not believe the trade off in reliability is worth it. And even through they feel better my times were no different with light springs then they were with factory ones.