This is coming from someone who has worked in the ski industry for many years:
The average, general public skier gets their skis shop tuned/stone ground way TOO OFTEN!!!
Unless you are a World Cup Racer or have severe (like core shot) damage, you don't need perfect looking bases for the skis to work effectively. You are just wasting your money even getting your skis stone ground once every season.
Again, unless you have severe damage, all you really need to do is to keep the base waxed and the side edges sharp with a few passes with a file guide.
When you buy new skis, check to see if the base is flat, you like the factory base structure, and the factory base edge angle is right for your intended style of skiing. If any of these parameters is not up to snuff, find an EXPERT tuner and have him/her do their thing.
After that, DO NOT get the skis re-ground unless you have severe rock damage. Those smooth, shallow grooves that you will get in the base from minor rock contact will do nothing to detract from the skis performance. The less you get you skis stone ground, the faster/better the skis will glide. The snow will polish the base better that any tuner can do! Also, DO NOT touch the base angle. Any minor dings can be polished out with a fine diamond stone. Like I said earlier, just wax often, and keep the side bevel sharp.
I have gone as long as 4 years before I need equipment reground. I am on the snow 80-100 days per year.
I know what some of you are thinking: "Then why does the shop suggest full tunes/stone grinds for my skis so often. The techs must know something about the skis that I don't" As an industry insider, here is a little tip: Ski/Snowboard full tunes/stonegrindes are almost PURE PROFIT for the shop. It is way more profitable to service the equipment that to sell the orginal skis! Most techs are trained to sell the customer a full tune even if the skis really only need a wax/side edge treatment.
Don't fall for it: Your skis will last longer, ski just as well, and your wallet will be a lot thicker too!!