I mainly refer to applied mathematics when describing my experience
Often I find that it is easier to grasp a concept from the author's slides than from the description in a paper. When one has to summarize their findings for a talk, they often end up with an exposition that gives a clearer understanding of the "big picture" and the nontrivial details. It is easier to separate what is important and what is not. If someone really needs more detail and rigour, they can check the paper, but I think that 90% of the readership would get more from the slides than from the paper.
Of course a real paper is still necessary, to provide details to the interested reader and to testify that the details work indeed (and the referees can certify it).
However, slides are typically difficult to find. Some scientists self-archive (a subset of) their slides on their personal web pages; some others are hidden in conference sites. No database such as Scopus indexes them. It is often tricky to match up a paper and its slides.
So, my question is the following.
Is there any journal that publishes slides together with their papers? Or slides only? Or, more generally, that tries to experiment and consider similar less formal media for presenting real science?