If you've got a product_image_location field with the image file name in it then I don't see why you'd need to search the images folder for any file with the product id in it's name - you'd just read the image that is named in the field.
Where the saving would come in is the fact that having a default "no_image.jpg" value would mean you wouldn't need extra logic to handle "products that have images" versus "products that don't have images".
You'd still need to keep that logic in place, just in case the image file named in the database isn't actually to be found, but with a default value in the database you'd be able to avoid wasting time trying to read files that you already know don't exist.
Then your only trouble would be if there was no "no_image.jpg" file..... 🙂
