The purpose of a durable power of attorney regarding property is to address situations in which you are still alive, but you are unable to manage your day-to-day affairs. If you have created a Revocable Trust as described below, and if all of your assets have been conveyed into the trust, then the durable power is unnecessary.
However, if there are assets owned by you individually (not in a trust), then in the event you become seriously ill, the appointee (as provided in the durable power) may act on your behalf without the necessity of a court action to have a guardian appointed for you. As such, I always suggest that my clients sign a durable power of attorney even if using a Revocable Trust in case something accidentally falls outside the trust.