Because I don't always believe these warnings, I failed to drain the oil after 40 days of non use and the next time I used the chainsaw the oil pump was inoperative and leaking.
Fortunately the pump was replaced under warrentee.
But is it usual to have to drain the oil if not used for 30 days? What if I use the saw for a minute or two and don't use all the old oil in the reservoir - does the reservoir still then need to be drained?
If I had known of this time-consumming requirement I probably would not have bought a chainsaw for occasional use.