You know, my recent leaving behind of the Lem's Goetia spirits may have left people thinking my approach to the Spirits doesn't have room for demons. Nothing could be further from the truth at all. The Hermetic System has plenty of room for Demons. They fit right into the cosmology. Recognizing they exist and are responsive to the conjuration techniques we use is essential for long-term success and the accomplishment of the Great Work. Ignoring their existence, not making room for them in your system doesn't eliminate their influence from your life at all. Plugging your ears and going "no demons no demons no demons" isn't going to result in acquiring the Philosopher's stone any more than an ostrich poking its head in the sand keeps it from getting eaten.
You've got to have room in your system for demons, that's the bottom line.
My personal opinion is that the room in the system should look something like this:
See? Plenty of room for demons!
Does that mean no Hermetic Magician should ever let them out to go to work for them? Heck no! If you need something done that you haven't acquired the initiations or empowerments to accomplish without the use of Demons, then by all means, conjure up the demons if you're that impatient. Jason advocates having a laser-specific goal in mind before turning to them, and that might help too.
But what I've seen is that the demons don't deliver what you want or need in the long term. I've found that turning to them for anything is likely to look really appealing in the short term, but eventually circumstances will arise that negate whatever benefit you received from them. You end up extending the problem, postponing some of the effects you want to avoid in the short-term, while adding more problems to clean up later. Eventually, and it might take a couple of years, you'll end up wishing you'd spent the weeks or months Working with nicer spirits with better intentions developing the resources and powers you need to accomplish the goal without infernal influence. Better to leave them in the vault.
I wonder sometimes though, whether my experiences with them has given me some level of protection from stupid magicians sending them against me. A couple were hanging out a month or two ago, and they went away when I noticed them and told them to be gone. They took some things that I needed, but they left.
The thing is, my HGA could have gotten rid of them too. So could my relationship with God. Or Michael. Or holy water. Or even the LBRP.
Nope, I really can't think of anything really useful that came out of my Work with them. Maybe there's something I can't see right now, but if there is... I don't see it.