[bluGill]

Start and stop does the most wear per unit of time, but constant motion also does wear.

Start and stop tends to cost a lot of energy, and high speed also tend to need more power. High speed also does more wear. Overall though, a small compressor on high speed 100% of the time is better than a larger compressor on lower speeds most of the time - but that isn't a realistic option as there are too many variables to allow choosing the perfect compressor size. So a oversized compressor running at low speed most of the time is generally best.