Unlike other wills, the pour-over will is not a stand-alone document. It is meant to be used along with a trust as a safety net and to do things a trust cannot, such as naming a guardian for your children.
A pour-over will can be used as a way to capture any items that may have been left out of another will as an alternative to a codicil/clause.
You cannot designate a guardian through a living trust. You will need to create another document at the same time to indicate who you would want to take care of your minor children in case both you and your spouse die.
This can be done with the pour-over will, which will be included with your trust.
Even if you have no minor children, you should probably create a pour-over will and name the trust as beneficiary to ensure the trust has all your unaccounted for assets.
Similar to a pour-over clause in a last will and testament which names a beneficiary for any unaccounted for assets, the pour-over will can capture the left-over assets and place them in your trust.