It is essemtial in commercial/industrial etc. and most jobs won't get signed of till the clip frames are on the wall, always a last minute apprentice job!
Don't really seee the need on domestic though, I have never seen a house with one and I have tested a lot! However with a lot of sparks doing paperwork on the PC now, would it really take more then 5 mins to make one up and at least give it to the customer with their invoice? (p.s. I dont work for myself, so tell me to jog on if you want!)
If the fuseboard labelling isn't clear, I can't help myself but to correct it after finishing testing!, even if that means tippex out!
Forgot to mention though, although I don't leave MCB's in, I don't really care or think its a regulation or even a 'best practise issue' Just a minor point!