Isn't this effectively neutral over time? Heat generated during compression, lost during decompression, so basically using the air as a heat storage medium?
So far so good, just the old thermodynamics. It gets interesting when you have a cooling use case anyways: then you can skip on some of the decompression recovery and use the "cold" from decompression directly, to cool down something that needs cooling, without going the extra way of converting back to electricity and then sending the electricity recovered into a compressor setup for "creating cold". Bonus points if you also have a use case for the heat you did not use in reconversion to electricity, but chances are between losses during storage and heating some the gas back some amount beyond neutral you won't have much spare heat anyways.