The only disk images of varying size used to be sparse bundles and sparse disk images. Now plain read-write disk images can also vary in the disk space they take, as explained here.
Precize
If you’re running any version of SilentKnight before 2.10, you need to update it now for compatibility with Catalina and later, particularly for Sequoia. And there are more essential updates too.
Update adds two new datestamp fields, and gives decimal seconds in times. Use this app to explore how macOS sets those on files, as shown.
Sparse files are now common among databases, disk images, and virtual machines. How they work in APFS, how they’re created, and how they can explode.
What is that text-encoded data embedded in so many Property Lists? Most are Bookmarks, and here’s how to decode them.
We’re almost unaware of clone files, and how they’ve changed macOS. But look at most documents that have been saved more than once, and you’ll see they’ve now be cloned.
Understanding how APFS works: inodes, attributes, file extents, extended attributes, and how they change with editing and cloning.
Adds a new feature that will resolve an inode number, such as that given in an APFS error or warning, to give you the item name and path.
When you run First Aid, its reports an error with an inode. Here’s how to identify the item responsible by converting that inode number to a file path.
How does macOS track Recent items for apps? In a property list, using a Base-64 encoded Bookmark. Here’s how to decode, resolve and discover their contents.
The Eclectic Light Company 