Like everything....it depends on a lot of variables, including, and not limited to, how often you ski and the range of conditions on the Lonely Planet and the level of performance you wish to achieve.. Some do it blindly once a year, others more, many rarely, if at all.
To a skate skier, the structure and flex is as or more important than the wax. In spring, wet snows, the reduction of suction via aggressive structuring will provide better glide than throwing expensive, 'fast' waxes on your bases with finer structures. For cold, dry snow, finer structure and lots of brushing. There are more thoughts and info in our Tuning Weblog.
With machine grinds, you are reliant on access and convenience to a competent tech vs learning to micro-managing by hand if desired. It's easy to increase or decrease structure by hand and minimize the subsequent re-saturation of wax needed.