Balance exists only to preserve itself.

Law/chaos, light/darkness, life(death, good/evil... All must exist on their fair share, and Balance can be a nallied or an enely of all of them, always allied with the weaker against the stronger, and often changing sides if the strenght relation changes (or staying aside if their Alliance will incline the power balance).

Of course, this does not make strong allies for them, s obeing used to rely only on itself, and all other forces see them as a source of aid in times of  need, but also as untrustworthy traitors, if they achieve superiority.

Shadow is a manifestation of Balance.

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Most of the cosmology I use among Law/Balance/Chaos triad is, more or less ,taken from Powers and Perils, and many references to the magic system will also be based on it, though I hope it can be adapted to any system.