If a couple is married or part of a domestic partnership, holding assets in joint tenancy is acceptable, but far from ideal. Married couples living in a community property state (such as California) can obtain a “double step-up in basis” (HUGE Tax Benefit), but most people fail to take advantage of this tremendous tax benefit by keeping assets in joint tenancy.

However, adding anyone else (besides your spouse or domestic partner) as a joint tenant can create other problems, such as:
The new joint owner could misappropriate the asset. After all, you gave it to them.
Did you file a gift tax return when you added his/her name to your asset? Adding a name to an asset is a gift that could subject you to gift tax liability and potentially cause adverse consequences with respect to the Federal Estate Tax.
Do you really want to expose your assets to someone else’s problems?
If the joint tenant gets involved in a divorce, bankruptcy or lawsuit, your assets may be tied up in a long legal battle and ultimately your assets could be encumbered, compromised or lost.
Joint tenancy means “automatic right of survivorship” so the surviving joint tenant will get the entire asset, regardless of what your Will or Trust says.