Probate Takes a Long Time in California and is Very Expensive.
Probate can take quite a long time in California and is typically quite expensive. The worst part is probate is totally public & subject to the oversight of a broken court system. It is only operative in the event of death and not an incapacity, so your loved ones could have difficulty getting access to your assets in the event that you were hospitalized & could not communicate.
A Trust is a Legal Document That Tells a Trustee Your Instructions
A Trust is a legal document that tells a Trustee (chosen by you as the creator of the Trust) how you want your assets to be handled if you are incapacitated or in the event of your death. So long as your assets are owned properly by the Trust, it does not need to be brought before the Court, so it's totally private. And, the person you choose as the Trustee has totally control over the process, which is often a lot less expensive and much quicker than the Court process called probate, which is required with only a Will.
You need to have both because a Trust only works if your assets are owned in the name of your Trust and sometimes an overlooked asset gets left out and it will be subject to the Will.