It all depends on snow conditions, the quality of your gear and of course the skier.
The most simple way to see if you need a tune is to check the base.
If your base is dark and smooth then you are looking good.
If it’s got a dry white-ish texture in the surface and looks rough then it needs some attention.
To check your edges carefully lightly run your finger tips down your edges, if its smooth like a knife edge, that’s all good! If its as rough as a grandads old file, then book it in for a tune.
If you’re still not sure, drop into the shop, its free to ask if your skis or board need a tune.