By default when you convert any nonstring value to a number, it will result in the number being 0 and throw an error. I'm not positive but I don't think throwing an error causes performance issues, and if your range of numbers does not include zero this shouldn't be an issue. If you need to include zero in your range, then you'll need to do some more advanced exception handling, which I personally don't know how to do with the trigger editor.
By default when you convert any nonstring value to a number, it will result in the number being 0 and throw an error. I'm not positive but I don't think throwing an error causes performance issues, and if your range of numbers does not include zero this shouldn't be an issue. If you need to include zero in your range, then you'll need to do some more advanced exception handling, which I personally don't know how to do with the trigger editor.