We used a couple of them last night at Waverly's at the Cannery. Our waiter takes them when we are seated and calls them in. (This particular place allows us to use 2 certificates when there are 4 people at the table, for some reason. ) We paid the balance using a comp from my host and cash.
We also tipped in cash, even though the certificates said 18% gratuity would be added to the bill before the discount. Our waiter didn't do this, because he knows we always tip him more than that, LOL.
The only time I ever had a problem was at Vino's in the Cannery, where they DID add the 18% gratuity and, because of that, told me I could not pay the balance with my Cannery points, because points cannot be used towards a tip. I explained to the server that we planned to tip in cash, and it would be more than 18%. She promptly got the manager, who changed the bill to remove the 18% tip so I could use my points.