In my experience...
Evocative magic is most often understood as intentional intercourse with spirits, typically intended to gain information not otherwise readily acquired, or to manipulate targeted circumstances that the operator wants to change. From the ceremonial magic perspective derived primarily from Medieval source material, the art tends to include selecting the right spirit for the job, in a manner of speaking. The literature on the whole tends to reflect a plantonic cosmological scheme, which in brief means a system of hierarchical categorization: spirits can be differentiated by species, and then ranks within each species, and individual spirits within a given rank, or something similar.
Within that context, individual spirits seem to be presumed to have an existence that is independent of the magicians who would summon them, and that is durable (perhaps even eternal). There is also, often, something of a place presumption in effect: the idea that when not in the summoned state, a spirit is somewhere else, in a manner of speaking.
To put a face on it, common versions of The Goetia list a number of individual spirits of the general demon or evil spirit class, along with their various ranks and personal attributes. A common modern approach to using literature of that sort to practice magic is to select a demon from those listings, the way a physician might consult reference material in selecting a remedy to apply to a particular manifest malady.
I'm interested in how closely those ideas capture your (anyone's) attitudes and/or practices, and/or in how and why your ideas and practices differ.