I agree with both Perky and BK, though I think I stand someplace in between. There *might* be situations where it proves useful, but in reality there's probably little need to go through the trouble.
The obvious upside would be that you could notarize deeds, etc., related to your clients' transactions. A quick read of the
California Notary Handbook (see p. 10) tells me this is legal, but gut instinct tells me that still might not be a great idea. (Consider the implications if someone alleges fraud in the transaction.)
I just let escrow handle the notary. Most of the escrow companies I know use mobile notaries to handle the more urgent transactions.