Rockers were getting nosy, have not adjusted them for a long ,long while. So that was todays project ,sound is better!!
If you're talking about valve lash, it can "improve" performance if you are way out of whack and the valves are staying open too long or not opening fully. Basically it will just get your engine back to running the way it should be, noise reduction is a bonus. It will also help with efficiency and temperature control. and remember to always adjust your valves hot!