When someone moves into a care home and their fees are being paid (in full or in part) by the local authority, they are not expected to hand over every single penny of their income. The law recognises that people still need a little money for the small but important things in life.

A best interest decision is a formal process used to make choices on behalf of someone who lacks the mental capacity to make a specific decision for themselves

If you are a loved one receives care and support that's funded by the local authority the personal allowance is what you are allowed to keep each week. It's not much but its yours.