If you can leave it open, do! Open elements are not bad for your pool. Keeping the cover closed for long period of time, traps the chlorine gasses and can cause cloudy water. No one wants to come home to a murky, stinky pool!
If you cannot leave the cover open for safety reasons: try and have someone stop by once a day and open it! make sure not to trap those gasses.
No cover? No problem! Just make sure to balance the water before you leave and when you return.
