Quote (PSPZorZ @ 13 Mar 2011 14:19)

Tuning down isn't necessarily useless, it really depends on what you are trying to do.
If someone is singing and has a lower voice they might want to tune the guitar down.
I use heavy strings (14s) on my guitar which puts a lot of tension on the neck, I would not dare tune my guitar to standard because of this I keep it tuned to Eb.
It also might be easier on your fingers to play a tuned down guitar (less tension) if you are a beginner.

So there are definitely reasons to tune the guitar down, but I'd say at this point your better off just sticking to standard (:

EDIT: By the way you earlier showed this as the scale:

Eb----------------------------------------------------------------
Bb----------------------------------------------------------------
Gb----------------------------------------------------------------
Db-----------------------12--15------------------------------------
Ab------------12--14--15--------------------------------------------
Eb--12--14--15------------------------------------------------------

The last note is a 14, make sure you are playing 14 instead of 15.. like this:

Eb----------------------------------------------------------------
Bb----------------------------------------------------------------
Gb----------------------------------------------------------------
Db-----------------------12--14------------------------------------
Ab------------12--14--15--------------------------------------------
Eb--12--14--15------------------------------------------------------