Although the free version of the plugin probably gives you more than enough to get you started, below are a few reasons you may want to upgrade:
- Ability to use two menus on the same page
- Ability to target mobile devices (using wp_is_mobile())
- Ability to use menu as the only menu on the site
- Multiple colour scheme options out the box to make setup easier
- Header bar creator
- Auto Height menu option
- Disable scrolling when menu is active