What is the difference between 2 users and 2 licenses?

My wife and I each have our own business and we each enter our own information on our own macs. At the end of the year, I access her files to handle taxes, etc.

I believe this can be done via two licenses (as we do now with Mac 2016) - as long as we do not access the same file at the same time. However, I notice that the two user version is less expensive than two distinct licenses; but it is somewhat unclear if there are any restrictions on the set-up of the two-user version. Is each installation of the 2-user version a full copy that can run independently on its own machine (e.g., on an independent laptop) or is the 2-user version designed as a single server install with 2 client installs (i.e., which would prevent both users operating independently)? Are there any other limitations of a single 2-user license that might prevent using it as I described above?