Profiles being active has a distinct effect on a translation unit being compiled. When contemplating the effect it has on a translation unit, users often perceive everything being proposed in a profile paper to be done only when the profile is active, leading to common misconceptions about what switching a profile can do. Terms I have heard from a dozen different interactions are dialecting, epochs and subset-of-a-superset. This paper defines what profiles can and cannot do, and what activating a profile can and cannot do, in the view of its authors. The content below, other than the "in short" section, is intended for the editor to editorially format as desired and be added to P4300, as guidance on what profiles can and cannot do.