By default, when viewing a diff (the difference between versions of a page), it shows the diff as well as the resulting page content.
There is a preference option "Do not show page content below diffs" ((tog-diffonly)), which makes only the diff load and not the page content. I don't know why it was introduced, but I enable it to reduce loading time, so I can browse diffs more quickly.
However, sometimes I'd like to see the content after the change anyway, for which I would then have to temporarily disable the preference.
Therefore it would be a nice feature (as part of having tog-diffonly enabled) to have a button like "load content" below the diff view, which then shows the content (i.e. on request, instead of always).