This is one that seriously gets me as to why we don't do this more, it would make so much sense. Obvious benefits are power generation, but also when you consider, it would significantly reduce how scorching hot large carparks get in the sun, depending on the style of the solar canopy being built it could also massively reduce the amount of water flow onto the ground reducing some wear on the tarmac in addition to some hazards.
Also for places like the UK where we typically don't have huge amounts/extended periods of snow, as long as the canopy is sufficiently designed for the additional weight, you could ameliorate the need to salt the car parks, once again increasing the life of the tarmac.
It would also keep people's cars much cooler, in the sun, and make things generally a lot cooler below the canopy.