Doing it the other way around, setting a fixed file size (MB) and unlimited image dimensions, will reject all attempts at uploading images larger than what's set as the max file size (MB) instead of allowing the larger uploads but resizing the images to whatever is set as the max file size (MB) and leaving the original image dimensions intact.
So what I'd like to see is the option for all the possible image permissions to be respected by the gallery itself automatically and not requiring the users to figure out how to work with the gallery's permissions because that's a) user-unfriendly and b) completely unnecessary.
I somehow managed to not notice this before: "Provide the maximum media file size in megabytes (MB). Media over this size will be rejected." but the bolded bit is really horrible from a usability POV. Rejecting uploads over something that can easily be automated is something that should never happen. When faced with upload fail due to that, how many people will just not bother with resizing their images and skip the upload altogether and/or not even know how to resize their images? Whatever the % is, we could easily avoid it.