From Good Ereader:
Where some publishers at one time were getting their feet wet in the world of digital publishing by experimenting with marketing their backlist titles as ebooks, the turnaround in digital sales has caused many publishers to now focus on the ebooks of their bestselling titles. But those backlists aren’t forgotten; on the contrary, technologically savvy publishers are now experimenting with using those backlist ebooks to add even more value to digital purchases by bundling several titles.
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The option to bundle ebooks can be especially helpful for smaller press publishers, digital-first or ebook-only publishers, or indie authors with a number of titles, as it helps with the discoverability while not forcing the rights’ holder to focus their resources on separate marketing strategies for each different book. Where reading consumers might be making the bundle purchase in order to receive one specific title, they are now more likely to read an author’s work that they otherwise would not necessarily have bothered with.
Link to the rest at Good Ereader