( Also why we need to do a valve job now and then.)

It is about combustion temperature. As the engine warms coolant and heads for the track, or road .the extreme heat expands the top of the piston and what was eccentric and tapered when cold, becomes more round and happy.

Same for the Valves and seats, although , as they are smaller, they are more prone to deformation. Thus, the more frequent Valve Job.

Your engine will live longer and stay happy, if you drive it until it reaches it's best Operating temp.

Then wail away , and enjoy.

Dr Porsche understood it a lot better than I do!