Sparse images: only use smart backup?

[sjk]

From Creating a disk image of a device, folder, or volume:

You can create a full disk image that uses the same amount of disk space as the disk it represents, or create a sparse disk image that includes only the data on the disk. For example, a 10MB disk may have only 5MB of data. A full disk image would be 10MB, while a sparse disk image would be 5MB.

Sparse images don't preallocate disk space in the filesystem, which definitely has advantages in certain situations; the example you gave isn't one of them. A drawback is that they need to be manually compacted to reclaim unused space.

In my current backup strategy I waste less disk space by using sparse images. When I store several on a single volume it means that no single image is using more space than it needs, which leaves room for the others to grow. That gives me enough flexibility to balance a limited amount of disk space until there's a real need to purchase more. And I can move images to smaller volumes which have enough free space for the sparse type.