Ladder has many advantages to NL.
Ladder has features such as upping runes, upping weapons + armors from normal to exceptional, and exceptional to elite. Being able to start fresh with everyone at the same time is also amazing, and truly brings the fun back to the game.
I love ladder, and will always play every new season. As a matter of fact, i always give away my shit to someone when my Ladder converts to NL.
No one knows for sure when the ladder will reset, unless of course blizzard states something official.