Observation

I don't do Crop rotation - just bung things into an available space!!

Same here! Something always fails to thrive, so spots open up for spare seedlings or a quick catch-crop of radishes or whatever. The German field marshal who came up with the saying "No battle plan survives contact with the enemy" was clearly a gardener

I find also that a lot of crops naturally rotate themselves, just because the place I planted them previously isn't empty when it's time to sow them again. For example I'll be following my broad beans with kale, so my Wizard field beans won't be able to go there in October. Instead I'll sow them where the outdoor tomatoes were, and the tomatoes will have to go somewhere else next May.