I agree with Sabato & Dick, although it does to some extent depend on particular circumstances.You can use your EPA without it being registered. The Court of Protection is only a 'means of making sure that you are doing everything above board, but they have said they don't get involved unless somebody complains to them.
I have not 'bothered' to register Monique's POA as I can make all things happen without at the moment. If we had to sell the house or make major financial changes, which required her signature, then probably registration would be useful but as Dick says - 'it is only to regulate that the finances are handled in the best interests of the patient.'
The POA is a legal document in its own right - registered or not. I think.