You can save points for Demonic Ritual, just know that rule probably won't exist once the demons codex comes out.
I just don't like using it, as you need a chaos character to not move the turn you summon, and I want my knights moving every turn.
The units you summon won't have objective secured, as they won't get demon army benefits, so won't help holding objectives (which wardogs are very good at). I just don't see a use, where having a knight on the table t1 won't be better at helping with.
In the old knights book, I didn't have ways of spending extra points, so brought in a change caster, so I could take abhor the witch, and still have a psyker, but I'm not doing that anymore.