It all depends on your circumstances.
Since I have to pay over 120 dollars to add 3-4 inches of water to my pool, live in a colder climate where every bit of heat is very welcome, I gladly use my solar cover all the time, it helps guard against evaporation and collects heat during sunny days, and retains heat during overcast days and at night l, allowing us to swim earlier and later into the season.
Those who can just throw a hose in the pool to top it up, don't really care for it's anti evaporative benefits.
Those with heaters and lots of money won't care for the heating benefits.