IMO it depends on the wheels and what you;re looking for. If these are knockabout wheels on a basic bike, and all you;re looking for is reasonably decent true consistent with the purpose, or a quick touch-up true for a low cost, then it doesn't matter, because odds are they can be trued decently enough with the tires on.

OTOH performance wheels that you;re looking to have properly aligned and tensioned, (ie. plenty of close tolerance tweaking), then the tires will have to come off, and it's between you and the mechanic, and whether he'll charge extra if you don't remove them before bringing him the wheels.

When folks brought me race wheels to work on I always preferred to get them without tires. I never minded removing the tires and didn't charge for that, but I wouldn't remount the tires unless asked specifically. That was because it was easier for the client to check the wheel without tires. For well glued tubulars, like on race team wheels, I'd leave them on for the entire job, and align based on the hub side of the rim.

(in my circle it's considered bad karma to remove a well glued tubular that wasn't punctured. Like with certain birds, tire and wheel were paired for life.