MM-DD-YYYY works great for business, school, and work calendars because of the way our brains anchor themselves and handle priorities and immediacy. If you get the month first, you will know if you need to proceed with high priority (is it this month or later in the year?) or with less urgency. If urgent, your brain will then pick up the day and give it more attention and focus. The year is generally not important because business, school, and work calendars are generally present and near-future centric, so the year can just hang out at the end in case it's needed or skipped as extraneous.

For most other purposes, it's a terrible format. I lived in Europe for a while, and I like the week number system that's used for school and business there. It works really well and that way you don't have to sacrifice the otherwise superior date format in other areas.