Yes, you would not be able to act on heach others behalf for the Isas or any bills in the others name, or sell the house, if the need ever arose. Just as important is the Health POA, should either of you need to make decisions on each others behalf. You would also need to do them before either of you lost mental capacity, also appoint a replacement POA(s) they would then act after the death of one partner for the or if you both lost mental capacity. They are easy to do on line on the Govt website.