In many traditions it very common to use a magical circle to make clear to the spirit world, the working space for the practitioner.
In Liber ABA Part 2 is stated concerning the magical circle:
“The Circle announces the Nature of the Great Work.
Though the Magician has been limited in his choice of room, he is more or less able to choose what part of the room he will work in. He will consider convenience and possibility. His circle should not be too small and cramp his movements; it should not be so large that he has long distances to traverse. Once the circle is made and consecrated, the Magician must not leave it, or even lean outside, lest he be destroyed by the hostile forces that are without.
He chooses a circle rather than any other lineal figure for many reasons; e.g.,
1. He affirms thereby his identity with the infinite.
2. He affirms the equal balance of his working; since all points on the circumference are equidistant from the centre.
3. He affirms the limitation implied by his devotion to the Great Work. He no longer wanders about aimlessly in the world.
The centre of this circle is the centre of the Tau of ten squares which is in the midst, as shown in the illustration. The Tau and the circle together make one form of the Rosy Cross, the uniting of subject and object which is the Great Work, and which is symbolized sometimes as this cross and circle, sometimes as the Lingam-Yoni, sometimes as the Ankh or Crux Ansata, sometimes by the Spire and Nave of a church or temple, and sometimes as a marriage feast, mystic marriage, spiritual marriage, “chymical nuptials,” and in a hundred other ways. Whatever the form chosen, it is the symbol of the Great Work.”
My personal view on the matter is this. Many practitioners using a physical circle painted on cloth or drawn with chalk on the floor or drawn in the sand. Which is fine and nice to do but for the serious modern practitioner not required as such. All considering this its in my view very important, or better, the most important, that one ‘is’ already a magic circle, realized it. By doing all the groundwork one isn’t very vulnerable any more against unwilling spirits.
What do I mean by this? What I mean is that when we are purifying our lower part (lower binary (Ruach and Nephesh), our lower self and submit it to our Higher Self or Holy Guardian Angel one is already radiating and this is in my view the ‘true’ magic circle. No lower entity or negativity can enter or carries away the practitioner with negative thoughts and deeds. The building blocks of this circle of light is the right motivation, a clear view on the matter, mastering of our thoughts, be aware of his/her own lower mind and is under guidance of the Higher Self or ones Holy Guardian Angel.
I know cases in which people think when they only use a physical circle it will protect them from harm of the ‘lower’ spirits they work with. Yes.., during the ceremony, but afterwards when the circle is down it bites them in the ass. Since the personality of the practitioner doesn’t deserve respect of the spirit world when not properly trained and ethically evolved . This explains that in many cases people evoke all kind of spirits for their pleasure or sensation end up in all kind of misery. So its more then important to work on ones personalty, purifies oneself (doing daily rituals like the LBRP or Star Ruby) , better control of ones mind, be more selfless, more compassionate, more noble etc in order to built a real magic circle of light. By the power of realization (what means actualizing a real circle of light) negative energies instantly were transformed or banned. Working hard being disciplined , becoming a better person and realize the Inner God is the best magical circle one can have.