A slideument is a cross between a slide deck and a document. The idea is that you can use a single slide deck both for slides during your presentation and as a handout for people to read afterwards. The trouble is that those two needs lead to very different requirements on your slides, so you can't satisfy them both. The result is that slideuments usually fail at both.
The main reason they fail is due to the amount of words and detail you need in the deck. If you want a stand-alone document you need enough context to make sense without the speaker being there. This requires a lot of words. But if the speaker is there, and speaking, then the audience ends up both reading and listening - and usually not concentrating properly on either. A good slide deck is a VisualChannel, it provides an accompaniment to the spoken words, reinforcing but not duplicating what is being said.
If people want a stand-alone document, then you can provide them with one - but it should be a different document, one that's designed for reading and not speaking.
The most sensible argument I've heard in favor of slideuments is that audience expects them, even if they are useless and never read later. I've a lot of sympathy with this argument, as it goes back to my first major presentation - a tutorial at OOPSLA in 1992. Since this was a big deal for me I decided to work hard to provide an extra-special contribution. So instead of the usual copies of slides, I wrote a special document to support the talk - about 40 or so pages - and provided that as a handout. That document was a much better coverage of the topic then the slides would be. But on the day I got lots of complaints because I didn't provide a copy of the slides. I am forever grateful to Rebecca Wirfs-Brock, who was the tutorial chair that year and backed me up.
People do expect slides, even when they don't really make any sense, and often it's easiest just to run off a PDF. I think that ideally you should try for more. My approach in later tutorials was to give out both the document and the slide copies. These days I give people my TalkNotes URI that points to relevant articles I've written on the topic of my talk.
Slideuments shouldn't be confused with Infodecks
The term Slideument seems to have been coined by Garr Renolds (author of Presentation Zen). A couple of worthwhile posts by him:
- Slideuments and the catch-22 for conference speakers
- Slideshare and the "slideumentation" of presentations