Give readers many editions in one package without tagging your PDF.
PDF makes a document portable by wrapping all its resources into a neat, single package. As people desire more features, more things get packed into the PDF. By attempting to make one file do all things for all people, that one file becomes large and unwieldy. Its portability begins to suffer.
In particular, Adobe has worked to add an information-oriented XML-ish layer on top of its presentation-oriented PDF features. The result is a single file that you can use for many purposes, such as paper printing, handheld reading, accurate text-to-speech, and accurate data extraction. However, creating these tagged PDFs is a slow and expensive process. The data layer is interwoven with the presentation layer, so accessing the data is difficult. Consequently, your readers have few options for utilizing this data. Finally, a tagged PDF file can grow to more than twice the size of its untagged counterpart.
In general, I advocate distributing a separate edition for each target medium. This is much easier on your readers and on your workflow. Eating sushi requires two chopsticks. Planar geometry requires five postulates. Some things shouldn't be reduced too far; don't feel compelled to make one edition do all things for all readers.
With that said, sometimes it makes sense to distribute multiple editions as a single PDF. For example, you might want to use PDF features such as encryption or digital signatures across all your editions. Instead of tagging your PDF, consider packing alternative editions into your PDF as attachments [Hack #54] .
The concept of different attachments for different purposes makes more sense to readers than a single, shape-shifting (tagged) PDF. Also, they will immediately understand the benefits of each alternative edition. "HTML Edition" means reflowing text, easy data extraction, and easy text-to-speech. "Tagged PDF" means little to most people, so you might add: " . . . that acts like HTML sometimes. You own Acrobat, right?" You will have a struggle on your hands, assuming your reader has that much patience.