Avoiding probate is usually the most significant benefit of holding property in joint tenancy. Gift tax consequences are also important.
When a parent adds a child to the title of property as a joint tenant, the parent has made a gift to the child of one-half of the value of the property. If the value of the gift exceeds the annual gift tax exclusion amount ($13,000 in 2012), it is a taxable gift which requires the filing of a gift tax return. In some cases a gift tax must be paid.
Consult your estate planning attorney for further information.