Generally no. If it's that close, you may hear a miss at idle. Running faster is normal when comparing a cold, but off choke idle to full temperature idle.
Softer? Do you mean decreased power, or sounds different?
Frequency of adjustement is going to depend on how you run the engine. For someone like me that stands on it all the time, pretty darn often. I might get a couple thousand miles between "Checks." About the longest I'll go is 5000.
For a daily driven grocery getter, annually or perhaps even longer. It's always good to check, IMO, every ten thousand if it's behaving itself, more often if you have issues. If it sits parked for long periods, I'd decrease the miles between lash checks.
I've seen slants in the 100k range that are getting checked for the first time. They still seem to run OK, but tend to have a sputter at idle from tight valve clearnances.
I set mine running, hot, but I have friends that set them cold static with excellent results. They have fewer bruises.
CJ