> Sometimes I’ve toyed with the idea of getting together with some friends and splitting the rent on a shared studio space but really I know I’d only show up a few days a month.

I am the same. I actually do rent a "hot desk" at a co-working space and I use it barely once a month.

I have probably used it more for a private bathroom in the city centre than for the desk.

The original goal was just to get me out of the house and an excuse to get into the city for a wander. But I almost always choose to actually work in the gardens or at a cafe en-route. I keep renting it because it is pretty cheap and is entirely tax deductable for me, and on occasion it has proven invaluable (rain, cold, noisy at home, need to work for more than a few hours in a row and need the commitment device etc).