There are cases in which Joint Tenancy can help avoiding Death Probate. For example, if one person in a married couple dies, anything they owned in joint tenancy passes automatically to the surviving spouse. But when that surviving spouse dies (or if they both die at the same time), the entire estate is required to go through the full probate process.
Joint tenancy has even more disadvantages in other circumstances. In a case in which parents and their children own assets together, joint tenancy does not protect them from probate, can result in unintended beneficiaries, and can create legal complications around gift and death taxes. Overall, joint tenancy is an extremely poor estate planning tool.