There are a few thoughts to consider in regards to checkering. At a coarse level it provides a gripping surface, but coarse checkering hides figure in the wood, so most checkering is fine enough to show the wood grain at least somewhat, but the checkering ends up not really doing anything for grip. On a cheap piece of wood that doesn't have any interesting figure, checkering adds what they call in art 'interest'. On a high dollar piece of wood checkering hides the figure, maybe in a most interesting place. On the other hand, well done professional level checkering adds value (and interest). Poorly done checkering with overruns into the border can ruin value.
I do not do checkering or stippling. There are people who specialize in those tasks. I wouldn't recommend anyone that tries to do it all: carving, duplicating, finishing, and checkering. Checkering is an art form all in it's own. For an important heirloom quality project you should consider checkering as a separate contracted item with a checkering specialist.
Checkering is done after oil is finished, as there are multiple sanding operations that occur in the process of applying an heirloom quality hand rubbed oil finish. You can find my oilling instructions here.
Here's a few recommendations for custom checkering specialists (but I haven't personally used any of them, and I don't know of any of my stocks having been checkered or stippled. Who wants to cover up all that gorgous figure?):