IW There's different kinds of sunshine and different kinds of cloud.... I didn't know that when I got my system.
Turns out that a high and thin cloud cover can actually be beneficial for solar generation vs some direct sunlight... because some of the light is bounced up into the atmosphere and reflected back down by the clouds.
Which is why it's often warmer when there's cloud cover and colder when it's clear skies.
Direct sunlight can also heat the panels up more, and heat can lower efficiency. It's basic physics and thermodynamics.
Also... some us just like seeing the data and monitoring how our systems work each month. I share monthly updates on solar systems with people, how that affects use, how many days I was effectively off grid and how the majority of my electric bills from April to Sept are all standing charges... which are set to go up when my fixed deal ends to 69p a day... or £252 a year for the privilege of being allowed to use expensive energy generated by wind and solar whilst being charged as if it was generated by gas.