The main purpose of the Row item is to be able to center your submenu content within a wider submenu panel. For example, if you are using unbounded submenus which expand to the extents of your viewport, but you want the content to be centered within a 960px area, you would wrap your submenu content in a Row item. You can set the width of the row container in the UberMenu Control Panel > Main UberMenu Configuration > Position & Layout > Submenus > Submenu Row Width
Control Panel – Row Width Setting
Centered submenu content on front end
Using Rows in the Appearance > Menus panel
Add a row as a child of your top level items and parent of the submenu content that should appear within the row to center that content.
Rows can also be used to separate submenu content into different rows, as an alternative to the “New Row” option. Note that a Row item is not required to start a new row, however, so this item should only be used when necessary.