I'm in NoCal (near San Francisco) and have an automated opaque pool cover so it's not as good for warming during the day (but we have solar panels for that) and only keeps the heat in overnight about half as well, but it does allow us to have our pool at 88F almost the entire pool season with gas supplementing only in mid-April to mid-May and mid-October to mid-November. Most heat loss is due to evaporation of water (both day and night) and not from direct heat transfer.
The other savings from using any type of cover (solar or otherwise) is in having a much smaller loss of chlorine from the breakdown from sunlight (UV). An opaque cover probably does better for this, but even a solar cover blocks much of the UV rays (which is partly why the solar covers degrade over time -- the UV breaks down the plastic).
You will also have less make-up water due to the lower evaporation. This is most helpful in areas that have restrictions on water usage.
And as alredy mentioned by others, you'll have less junk fall into your pool water which helps reduce maintenance on cleaning traps and keeping more stuff out of your filter.
Finally, you should also find that with a cover you have less of a tendency for a rise in pH over time, though this is also dependent on your TA and pH levels. The cover helps keep the dissolved carbon dioxide (carbonate) in your pool and slows down its outgassing which would normally cause a rise in pH.
So yes, a cover can be a PITA, but it has a lot of benefits. We got an automated cover to remove the PITA aspect with some loss of benefit (thermal efficiency), but found it to be well worth it.
Richard
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