Do you mean this specifically with respect to cartridge bottom brackets, Andy? I've always believed that they are basically consumables (which seems a shame, but...) and that there is therefore no "required maintenance".

I'm midway through 'annual service' on a Brompton, so I'm not trying to put off maintenance - but I have resisted buying the tool to remove the BB on the grounds that there'd be nothing for me to do to it at this point. What would you do - clean, inspect and regrease threads?