What does a guardian of the estate or person do?

A guardian will always act in the best interest of the person. A good guardian will take into account the wishes of the person when making decisions about residence location, medical treatment, or even a job opportunity. You might question the necessity of a guardian if the person is capable of working. This can happen often.
An example would be a child with Down Syndrome. Upon turning 18, a child becomes an emancipated adult under the law. After turning 18, parents no longer have the right to make decisions for their child or the legal right to sign documents on their behalf. While many with Down Syndrome can make informed decisions and simply need guidance from others, some cannot. A guardianship can be appropriate in some situations to protect a young adult from having their rights violated or ignored.