Well, I am astonished about how much response there has been to my OP. Clearly the vast majority of commuters use full mudguards mostly all year round, but those that dont seem to be adamant that they are a waste of time.
It still confuses me that well respected brands like Decathlon advertise their flatbar road bikes as fast commuters, but dont even have eyelets for guards far less fitting them as standard. Why not??
You may have answered your own question. A lot of cyclists either don't mind or just don't want mudguards.
I imagine those bikes Decathlon bang out as 'fast commuters' are selling pretty well.