[Zubersoft]

MobileSheets will stop the crop the second it hits a non-white pixel (it doesn't have to be pure white, as there is a small threshold). If you enable the aggressive cropping, then it will only stop if it hits a large block of non-white pixels. In both cases, there is a small margin applied to the cropping region to allow for a small amount of white space between the edges of the page and the content on the page. This is so that you don't have things on the very edges of the screen. I don't provide options to control this margin, but I know a request has been made previously to provide an option for that, so it's on my (very large) list of things to do.

Mike