We do a lot of one-off requests, and we make use of both Project Templates and Layout Templates for them, since a lot of the projects start from the same basic map, or include many of the same reference layers, and need to have certain things in the map surrounds when exported.
We do have a few other cases where a specific person/department will routinely ask for different maps in a single "theme". In those cases, we'll have a "Planning and Zoning One-Offs" project and clone / reuse layouts as needed.
Map files are nice, but mostly useful for bringing a map with multiple layers across to different projects. Layer files, similarly, are useful for bringing single layers across to other maps, whether in the same project or not. There's a place for either one, really, but I personally prefer saving the map itself, as that will also include other things like the map's projection, reference scale, etc., that you don't get with a layer file.
You can also save map packages to AGOL / Portal, which is nice. If you open a map package from Portal, it keeps a link to the source package, so if you ever re-upload the same map package, Pro will prompt you to update your copy of it locally. Useful if you have multiple staff / machines in the mix.
- Josh Carlson
Kendall County GIS
