I think there's a bit of confusion as to when EPoAs do come into force: an EPoA for personal care and welfare can only come into effect at the point the individual is determined as mentally incapable, whereas that for property can be enacted by the individual at any time they choose or is enacted at the point they are determined as mentally incapable (the individual can elect in the document how it will function in their particular situation).

Any quick search would confirm this, eg from Community Law's website:

• Enduring power of attorney for personal care and welfare (see below in this section, “Enduring power of attorney covering personal care and welfare”). This kind of EPA can only come into effect when the donor loses mental capacity.
• Enduring power of attorney for property (see below in this section, “Enduring power of attorney covering property”). In this kind of EPA, the donor can specify whether the power comes into effect immediately, or only when the donor loses mental capacity.

The ability to elect to have someone manage your 'property' under an EPoA is certainly useful prior to being declared gaga - eg, I hold it for my mother, and having this already enacted makes managing her finances easier, given she's developing dementia but in many ways is not too bad. As such, we've not had to push it to the point where she could well be declared not mentally capable - the process of doing so would have significant consequences for everyone concerned!