Minor edits exist so that Wiktionarians can mark their edits as unworthy of interest from anyone else. It should be used only when the meaning of the page has not changed much, if at all. Dictionary entries are, by their very nature, short and succinct, so even changing a few words can have a major impact on the page, and in such situations it is considered bad form to mark a "major" edit as minor.
Use "minor edit" 
- When only changing formatting, perhaps indentation, or adding the ---- between languages.
- When merely correcting typos, or spelling mistakes, though if there are lots of these the edit may become major by cumulative effect.
- When checking a translation that is obviously correct, though don't if you are adding a new translation.
Major edits include 
- Anything that you are not sure about.
- Making changes to more than a few words, or altering the sense of the definition.
- Adding information to the entry.