After a snake eats something (and therefore as a large lump), it makes it more difficult for it to escape if it were attacked, etc. If you stress the snake during this period, it is very possible that the snake will regurgitate the food so that it may escape if needed (this is a natural response). It's not something that you want to do to your animal.
Why would it be beneficial for the snake? What could the snake possibly get out of being handled whilst digesting food?