If you want to add new photos to your website regularly or need to update images of stock items then it makes sense to be able to upload new images yourself. Having an updatable photo gallery allows you to add an image instantly without having to wait for or pay a designer.
Your image gallery's look will be designed and from then on you can upload the new photos or delete outdated images at the click of a button. You don't need any special training to be able to use the system.
You can have multiple image galleries for different ranges of items and categorise your photos to appear in the relevant galleries.