There is a lot of reasons why one has to renovate the pool. Loosing water is surely the most important factor, but also damages in the grouting, in the tiling, in the filtration system, in the ilumination or the cover.
But not only problems should animate to go for a touch up, also estethic and design motives influence more and more. There is plenty of posibilities to tune your once pride of the property, which might now be only a huzzle to clean and spent money in maintening and desinfeccion.
I do know clients, which were seriously thinking of feeling the pool up and making terraces, gardens etc. out of it. Think: How much more worth is your property with a pool? A pool, of course, which is in good conditions!