A will alone will not bypass probate.
Further, if the gross asset value left outside the will exceeds the probate amount (currently $166,250 in California), those assets will be subject to probate.
A pour-over will catches anything inadvertently left out of your trust and “pours it over” to the trust.
The pour-over will supplements your trust, just in case. This is also the document where you would designate guardians for your minor children or disabled adult children.