[yetanotherjosh]

Are you asking the use case for relative line numbers or for the plugin? For relative line numbering, the benefit I see is the ability to move with precision to specific lines without (a) switching to line-wise selection mode during visual selection, or (b) losing your horizontal cursor position, both of which are required for using the :<line number> jump. As for the plugin, it just makes switching between relative and absolute numbers conveniently automatic.