Magickal circles, as with all the tools of the trade, are foci to help the magician to change their own state of mind and shift from a normal waking consciousness into a more trance like state where they can better perceive ethereal beings that would otherwise not be detectable in the physical in all but the most extreme circumstances.
But, there is also the issue of formality here, which is mostly what we speak of. Its formal to make a circle, and theres nothing wrong with doing so. But its like being forced to wear dress cloths or formal wear at some mundane event; you dont NEED to dress up to talk to the people or walk around, but its a sign of respect to just do so when you are expected to. I think the same applies to some degree generally for magickal communication at least with brand new contacts.
It also shows a contact that you are willing to go out of way and put in time and effort into setting up something nice for first, second, etc contact with them.
The relationship with the contact in question is also important. If its strictly a business relationship, just as in an earthly business, each side expects some things from the other just as a sign of mutual respect. In that case a formal ritual for contacting once a good report is established would probably still be wise until the spirit says otherwise, and perhaps becomes more than a business contact and moves towards being a friend or otherwise. Theres also no harm in asking how that spirit would prefer being contacted, just as you might do in the physical to a business acquaintance.
If you are friendly with the spirit, a lighter atmosphere after the first several communications is OK, and youll feel whats OK to do and whats not. A circle is probably still a good idea, because its one of the most basic implements and just shows that you respect your friend still.
The relationship could grow to even more where no ritual at all would be needed, but never assume that to be the case; always use your heart to sense that. It will be the distinct feeling of “it is no longer necessary that I do all this”, in reference to the ritual, while you are performing that ritual, and is specific to the entity being contacted.
A relationship that is of a mentor/student quality is one where formal evocation may not be necessary, unless its related to what you are being taught, thus the circle may not strictly be necessary at all times.
If are you blessed with a loving and/or familial relationship with an entity it can be that all you have to do to communicate with them is think of them, and they are there… Or just remember that they never left.
So all this comes down to two things concerning the magick circle, and by extension, all magickal tools. One is its utility as a focus object, which is always good to have something as for your own personal benefit, and two, as a formality issue and a showing of respect that you are willing to put in effort and time to establish communication. Nice incense, some colors that the spirit supposedly likes, maybe even some artifacts the entity is said to associate with (crystals its said to like) etc, same thing.
Being creative is appreciated a lot too, like making your own circle out of objects special to that spirit.
It really depends on what kind of relationship you seek to attain with that spirit. If its just business, then keep it formal, respectful, and official. The spirit AFAIK will always respect that.