YSK because the first hot spell is when most people discover their AC unit is broken.
Several years ago I waited to turn on my AC. This is how I found out about one of the busiest times for repairmen and had to sweat for two weeks. Now I do a test run a couple of weeks before it heats up. Same goes for the furnace at the end of Autumn.
Edit to add: YSK line (Rule 2)
Second this. Keeps the unit in good order, you find out about issues before they become major problems, and it’s usually fairly cheap like 50 bucks. The downside is it’s a good opportunity for an unscrupulous tech to overplay some minor issue to try convince you to upgrade.