In Disk Utility, what advantages do "read/write disk image"s have over "sparse bundle disk image"s?
From this blog post:


  A customized .sparseimage file can be made larger than the total capacity of the physical volume on which it originally resides.  While the sparse image volume will seem to make that capacity available, attempting to exceed the physical capacity of the underlying volume will result in a disk error: "ran out of space."


A couple of other disadvantages of a sparse bundle:


Since it's actually a directory containing multiple files, it can't be attached to an email, sent with DropSend, etc. You would have to compress it into an archive first (eg. Zip).
It's only supported from OS X 10.5 (Leopard) onwards, so if you have an old Mac running 10.4 or earlier, you won't be able to open sparse bundles created on newer Macs.