Waxing frequently makes the skis run faster, and can protect and prolong the life of the bases. Waxing too often is not a bad thing, unless using high-fluoro waxes which can dry out the bases.
Frequent edging, on the other hand, whilst keeping the skis sharp and grippy, wears out the edges as metal is removed each time. When tuning the edges often, it is important to shave off the minimum amount of material, using a diamond file for example. This way it is possible for the edges to wear more slowly than if they were filed extensively from a blunt state after being left for some time.
A well tuned ski feels very different from one that is not, and so the simplest answer as to when to service skis is when they feel like they need it.
The table below shows how often I would tune different types of skis in my collection. It might act as a rough guide, but should also illustrate how much variation there is between skis I use for different purposes, and between skis where precise performance is more or less important.
|Race Skis, used for racing or race training.||After each day of use|
|Piste performance skis, detuned race skis or carvers||Every week or two|
|Freestyle skis||Once or twice a season|
|Off piste or touring skis||When they feel like they need it, i.e. when the edges are blunt or burred, or lacking grip on firm snow, or when they run slowly on flat sections|