Your experience my differ, but most SE bots that hit my server just get web pages alone. They, or their sister-bots may return and get image files, but almost never get pages and images on the same visit.
So my assumption is that any bot doing both during the same visit would not be a SE bot, but have a different agenda. Whether that is beneficial to one's interest or not would vary from site to site.
That said, I tend to block almost all bots except the top several SE bots, then just allow a few others as they show a benefit for my site.