For example if you have a heal spell which can target any ally (with the heal being the primary effect) and a secondary effect with <ApplyToCaster>1</ApplyToCaster> the following happens:
Cast on Ally that is not oneself: target gets the primary effect, caster gets the ApplytoCaster secondary as on would expect.
Self cast: ONLY the ApplyToCaster effect is applied, the primary effect is skipped.
