Pleasant Hill's early century housing stock was widely divided into suites well before current permitting rules existed, so a generic online estimate treats the neighbourhood as uniform when the actual variation between properties is significant. An agent who knows the streets can tell you which blocks carry that risk and which don't.
Local knowledge also means knowing which lenders will finance a specific suite configuration and which comparable sales in Pleasant Hill actually match your property, since the city benchmark of $444,700 tells you almost nothing about a single converted character home.
That kind of street-level judgment is exactly what an algorithm cannot replicate. Get your hand-reviewed valuation from Joel Dyck.