These data are used when the registration type is Trust or Corporate. If the client is set up as a corporation, then address and name information will be drawn from here instead of the general client information page.
If the form's registration type is custodian, UTMA, or UGMA, then by default the "FBO" is the minor and their social security number is the trust tax id. However, any minor may be inserted manually under these registration types from insert buttons.