A Power of Attorney document allows you to choose what your personal representative, or attorney-in-fact, will be responsible for by designating certain powers to them.
A Power of Attorney is also not like a bilateral agreement, it is more of a unilateral description of what authority is permitted by the principal.
The principal will also be able to choose how they would like the Power of Attorney to go into effect - for example, if they would like it to start at a specific date and last through incapacity, if they would it only like to begin if they are incapacitated, or if they would like to have it start at a specific date but end in case they are incapacitated.
Most states will recognize any POA that is validly signed in another state. So if you make a valid document while living in one state and then move to another state, your document will still be valid in your new state of residence. However, it may be a good opportunity to update your document and prevent it from being “stale”.