Okay, so:

If you 'bless' a demon, there is a slim (1/10) chance that you gain a 'demonic ally' and if you bind an angel there is the same chance that you will gain an 'angelic ally'.

The battle would end with 'with it's last ounce of strength, [insert name] submits to you and the angels/demons.' You will gain karma if you are with heaven, lose some if you are with hell.

The way they help is when you battle within the rest of the month, at the beginning of the battle it may say "[insert name] is battling with you, on your side" throughout the battle, your ally may attack '[insert name] attacked for [insert number]'

If you ally with all of the angels/demons you get one of two achievements:

'Peacemaker' for Angels

'Making of a Legion' for Demons