In general, the guardian has complete control over the financial, medical and personal decisions of the ward. This includes where the ward will live, how the ward's money is spent, and making routine medical decisions for the ward. A ward has no more authority to make these decisions for themselves.
The guardian also has the responsibility to account for all of the ward's income and expenses. In the beginning of the guardianship, the guardian files an inventory with the Court of all the wards assets, and after that the guardian files an annual accounting with the Court showing how much money came in, where it came from and where it went. At the end of the guardianship, the guardian must file a final accounting with the Court.
Being a guardian is a big responsibility, and not one to be taken lightly. If there is time to plan before a crisis, you can save so much time and money, and prevent a lot of family conflict, by having some straight forward documents executed that spell out your wishes. If you think your aging parent needs a guardianship, your lawyer can work with you to accomplish that. What plan do you have in place in the event of your own incapacity?