Reducing lag? I bet the opposite.
You see, welding, and pretty much any constraint on your construction adds another calculation to the physics engine on the server.
There is really no point, and I highly advice any smart builder against it, to weld and no-collide props with each other that are not directly next to each other. Because those props never get close to each other and never will collide anyway. So adding a constraint (may it be weld or no-collide or anything else) will only add more unneeded stress to the server.
The only tool that would really help against huge constructions, would be the parenting tool. Which basically disables physics on a prop and makes it a decal, which reduces stress to the server massively.
TLDR: Be smart and limit your constraint usage by constraining your creations manually. Do NOT use mass-constraint tools that add 50+ useless constraints that only increase server lag.
