A revocable living trust can achieve many things for its owner in terms of meeting estate planning objectives. There are some things, however, that only a will can do. For those who want the benefits of a living trust, a pour-over will can be an invaluable companion to your trust. Your pour-over will can make sure that your goals are protected in case an asset (or assets) didn't get funded into your trust and can also give you other benefits that are unique to wills, such as the naming of guardians.
Batman had Robin. The Lone Ranger had Tonto. And Sherlock Holmes had his trusty friend, Dr. Watson. Each of Robin, Tonto and Watson were trusty companions whose presence allowed Batman, the Lone Ranger and Holmes to be more effective at accomplishing the goals they set out to achieve. An estate plan with a revocable living trust can achieve many goals, potentially allowing you to avoid substantial expenditures of money and time. But, just like these fictional heroes, your living trust is more effective when paired with the right companion. In this case, that companion is a pour-over will, a vital tool for making your estate plan as complete as possible.
Your pour-over will can serve many vital needs. Perhaps the most obvious one is distributing some of your assets. If you have an estate plan with a living trust, then ideally all of your assets (that you have not already planned through other means) have been funded into your trust and would be distributed according to your trust's provisions upon your death. Real life, though, is not always ideal. For example, you could purchase, inherit or otherwise come into ownership of certain assets shortly before your death and not have time to get those new assets transferred from your name to your trust.
Alternately, you could have certain assets that you own about which you simply forgot, or maybe even never knew they belonged to you. Regardless of how it happens, if you have assets you own in your own name (that are not subject to other non-probate distribution), then they must be dealt with somehow. Your pour-over will directs that, once the probate process is complete, these assets go to your trust. At that point, they can be distributed according to the wishes you put down in your living trust document.
Why is this so important? Well, if you have assets outside your trust (items you own in your own name) when you pass, then those assets are generally part of your probate estate (unless they are things like transfer-on-death accounts that are automatically distributed upon your death). If you have assets in your probate estate and you have no will at all, then those assets are distributed according to your state's intestacy laws. This could mean having valuable assets being distributed in ways much different than what your goals are!
Your pour-over will also provides you with certain benefits that only a will can do. If you have underage children or children with special needs, you cannot name a guardian for those children in a trust document. You can, however, include your preferences regarding guardians in your plan's pour-over will. For those in that situation, this bit of planning is often a "top priority" in terms of goals to be accomplished.