A power of attorney has two parts and to complete Part 1 you must have the capacity. Without capacity the only avenue left is the court of protection.
The court of protection is much lengthier and costly process and so setting up a power of attorney is a sensible idea even if there is no immediate need for it. It also allows another to act for you immediately if you suddenly experience ill health or are temporarily incapacitated.
It is important to understand that setting up a power of attorney does not mean you cannot still make your own decisions, and the attorneys must help you with this process even if they think your decisions are unwise ones.
A power of attorney can only be used if it is registered and it can take several weeks to register a lasting power of attorney. This is another reason why arranging one might be very useful in the long run. If you lose mental capacity, your attorney would not be able to act for you while the process of registration is taking place.