When I have a crop already selected in the crop & straighten tool, I find it unexpected that when I change the aspect ratio, the crop changes to centered but maximally-expanded. It would seem more natural to me to relate the new cropping to the existing one, eg. by keeping the same center point or the same lower-left point, etc. Of course the boundary cases where the new selection runs into the edge of the image would have to be handled, but when I eg. have original (3x2) selected but want to recrop for an 8x10 print, I want the selected region to pretty much stay the same, which is more difficult to get right when I have to start from scratch instead of making minor adjustments.