Why summon demons???

it's true, demons can definitely help you.

The only problems I have had was when I accidentally stepped over some red tape with them, but that was easily fixed. If you do work with demons, I would recommend befriending a high ranking demon as a patron and using that relationship to help you understand them and work with them. If you show them respect, they usually will too.

If I were to summon demons it would be to gain more knowledge applicable to magic in order to gain power, and knowledge.

Based on my experiences, demons are actually truthful, and they never seem to have their side of the story told. See this all happened with a war between angels and demons. I personally met a demon and he was actually pretty cool. :) Once you get to know a demon your mind will change.