I last checked the valve clearances 65,000 miles ago and don't plan to do so again.
The valve seats get deepened as the valve hammers at them gradually closing the gap. At the same time, the cam follower wears opening the gap.
The two processes are very slow and take place at a near-identical rate keeping the gap within spec. At least, that's been my experience for the first 115,000 miles, after that I tend to fit a new engine as it's easier than changing the camchain and the gearbox is usually pretty baulky by then.