To support the people reviewing a pull request, it is handy to be able to attach screenshots, or even short videos (animated gifs) that better describe the new functionality.
We use Github in many of our projects, and now that one ended up using bitbucket. Their limit for files is 25Mb, and 10Mb for images, where Bitbucket has 1Mb.
Please do consider raising the limit from 1Mb, as it would help a lot.
It would obviously be a big win if we could have support for video in some way as well.