I think there are a few classes of presentations where good slides can still convey 80% of the content of the presentation.

They tend to be meaty technical ones, which is the kind of thing lanyrd would likely be heavy on with all of the tech events they have.

Presentations with lots of live coding are likely not worthwhile.

Slide decks posted after an event can be extremely valuable for the people who were actually there in the room as a memory aid - I often say "you can review this code sample in the slides later" when I'm speaking for example.

I find I can often get a lot of information out of reading slides, even decks that clearly weren't designed tomb viewed without a speak. It helps to have a good understanding of the subject matter though.

Finally, if a video of a talk is already available it can be useful to flick through the slides first before committing to the 30 or so minutes it take tomwatch the video, to confirm that the material is likely to be interesting.