Having a way to auto-crop an image to a specific size via a collection image's properties would save the need for a second thumbnail upload in a lot of cases – and the need for client having some way to crop images for thumbnails.

If you want to create a grid of collection items for a listing page and the images are all different proportions it obviously looks a bit messy. You can use 'image as background' technique to create item thumbnails but images are not optimised and can lead to large page sizes.