Isn't it expensive to operate a pool dehumidifier?

Yes and no. Yes, in that it costs more in terms of electrical energy than not having control over the space. No, in that the costs of operation are more than recovered in terms of the comfort to users, the preservation of the investment and the overall long-term value of the facility. The costs of not maintaining control can range from annoyance (condensation on windows) and reduced satisfaction (uncomfortable conditions on the pool deck) to loss of business (customers choosing another health club or hotel) to catastrophic building damage (mold, mildew, rotting timbers, stained walls, insulation damage, window replacement, etc.).