Who can see your viewing activity?
I use the "never drop" feature for important things, like my "Syllabus Quiz" in the quiz categories.
It's also helpful if you have one thing in the category that has a different point value.
Specifying the file types is especially important if you're not on a mac: If it's submitted as a .pages even SpeedGrader won't open it.
Also note that if they submit directly through Google drive (e.g. using turnitin) it tends to convert it into a .pdf
can you do this with quizzes too. ie hide grade