Yeah the protection of not for the entities you invited into your space, it’s to keep your meeting private from all the astral riffraff that want a free slice of your pie.
Doing magick sort of lights you up on the astral, and depending on the energy you produce, attracts various things that would feed on it. More than that, they then turn to you and attempt to attach to you, make you produce more and more and basically treat you like a all day everyday free buffet.
We call them parasites around these parts, and they’re the astral equivalent of ticks, germs and leeches. You wash your hands irl, and so, you manage your spiritual hygiene as a mage. Cs if you don’t, you could get sick. And by sick, I mean, like in the physical in the worst case scenarios, dead.
It’s low cost and high reward to take protections seriously. Nobody wants ants in thier picnic 
This kind of working is VERY attractive to hags and lesser entities that feed on emotional pain, longing, frustration, anger, envy etc.
The getting started guide with all forum orientation stuff, links to tutorials and popular megathreads are here: GETTING STARTED GUIDE, Rules, Notables, Tutorials and References. The links in that megathread are forum-made tutorials for things like spiritual hygiene, developing your astral senses and avoiding impostors and parasites.