There's a sort of black goop that forms from brake pad residue gets on my wheels, crank arms, and chainstays, and chainguard. It mixes with the oil that drips from the Sturmey-Archer. If it gets wet, then it oozes everywhere, and can get on my hands and clothes. So I wipe it off with a rag whenever I inflate my tires. I also wipe down anything that's accessible whenever I service the bike.

I'd trust my bikes to be safe and reliable indefinitely without any special attention paid towards cleaning. Naturally that will change if I get into winter riding.