I don't cut many through dovetails with a handsaw, but if I did, they would be cut to the line. Even if I'm using a backsaw for cutting small things, I'm cutting to the line and expect the cut to be the finished cut.

Look at that picture of siding in my earlier post. If you cut one a little long to force it in place, the one below it will be opened up. In fact, they're all hanging on their nails in predrilled holes. You can take a finger and push on any one, and it will move in and out some. That's not just those in that picture, but every one on any house I've built.

Anything less is just wasted effort. I build stuff for a living. Wasted effort doesn't work.