Invocations goal is ultimately partial possession. Invocation is generally reserved for spirits that we have a more intimate working relationship with. You don’t want some rando taking your body for a spin. However always make sure that you have a good rapport first. The purpose of invocation is to add a spirits power to our own for the purpose of spell work, or to learn more about a given spirits dominion or essence by merging with the entity for a short time.
Contrary to what many preach, invocation in my opinion, is a more advanced practice then evocation. Invocation leaves a mark on you every time you do it. It changes your energy to match the spirit you are invoking over time. So if you are doing heavy self work, and want to change your own behavior, then do invocation, not evocation. In invocation, spirits are like our role models… who do you want to be like?
I invocation is also damn useful for self healing. As the spirit is directly melded with your energy, so they can make whatever changes they need to make you whole again. Is it dangerous? If you are reckless with it and just invoke whatever comes around then yes. But if you want to work very deeply with one spirit in particular, then no.