These are reasons just off the top of my head:

1) To go through the process just to learn.

2) To standardize all my effects pedals so I only have to carry 1 type
of extra battery, therefore minimizing carrying space and weight and
minimizing the chance I will be out of the one I need.

3) The standardization will also eventually allow me to work on a
project that allows all my pedals to run on a power supply that accepts
multiple pedals. The power supply works with pedals expecting 9V. I am
unclear if it would work with pedals expecting 1.5 V... I have my
doubts, therefore the conversion project.

4) The 1 AA battery dies quickly.

JeffM wrote:
...modifying it from a 1.5 V battery to a 9V battery.
GuitarPsych


Seems like a dumb idea. A cell is much cheaper than a battery.
What advantage could there possibly be?