I'd think twice about using that shop for anything if they can't tune the bearing preload on a simple cup and cone hub following a servicing. It's pretty easy to do this and make it roll at least as good as when the wheel was new. It's fussy and takes some time due to the trial and error manner of fine setting the bearing preload but it's hardly rocket surgery....

Cartridge bearing hubs are another matter. In this case it's leave it alone until there's a rough feel and then replace. Some seriously dedicated or fanatical folks will carefully remove the inner seal on their cartridge bearings and grease the balls at intervals. But frankly for most of us it's more trouble than it's worth. Such bearins typically go a good 5 or more years before failing. And they are fairly cheap to replace.

But for cup and cone bearings, which is most if not all that Shimano sells, doing a strip and clean every few years is a wise course of action. There's certainly no need to do it annually for the reasons mentioned by cycommute and others. But over time, and especially if you ride in wet or muddy conditions or wash your bike at all frequently, water and grit will get in and build up in the hub. For bikes ridden in dry conditions and washed carefully and not that often you can easily go two or three years between servicings. But I wouldn't leave it much longer than that.