1. If you want to borrow my car, you have to follow the rules. First, you must obey the speed limit, fill up the gas tank before you bring it back, and bring it back before I need it tomorrow. Last but not least , you may not drive it if you have been drinking alcohol.
2. John accomplished a lot in his lifetime. He was a teacher and an activist for the poor, he wrote several books, and last but not least , he raised four successful children.

The expression is used before the last in a series of items to indicate that it is not less important for being last. Usually the series has been randomly arranged and no specific order of importance has been assigned to the items.