Emerge can be a powerful mechanic, as Elder Deep-Fiend has shown us in the past, and there are probably some shenanigans you can do by giving all your stuff emerge
Plus, it doesn't remove itself from the game so you can get it back with Regrowth, Yawgmoth's Will, and other graveyard recursion cards (including Gaea's Blessing, further down on this list)
Its very easy to remove her before this happens, given her total lack of protection
That means if you add a red mana during one step or phase, you can spend it during a later step or phase, or even a later turn
Necropotence cleanly draws a ton of cards given your life gain potential
Trading card games are pretty expensive and committing to a whole new game from start is not a easy choice to make