This might be kind of a tall order and even very complicated, but here goes:
I travel to Minnesota each year to visit family. Its been decades since I lived there and my geographic knowledge has dwindled.
With that in mind, it would be kind of nice to know what sites/towers cover what areas. For example if I'm in Minneapolis city limits, what sites/towers should I program? The occasional visitor may not know Hennepin East/West, Minnapolis city center and Minneapolis NS are good choices.
Not to derail the thread but this would be a really interesting long-term project for many systems -- essentially a survey of the talkgroups seen on each site to include the level of activity (i.e. talkgroup 12345 has 2500 hits over 24 hours on site X but only 50 hits on site Y and 25 on site Z). However, then there needs to be a place to capture/post that information... a whole 'nuther problem.
In many cases, you'd expect that the site(s) closest to the TG user to be the site(s) to choose but that isn't always the case - particularly with system where multiple sites are overlayed like Tx WARN and Philly PA (for example).
Ok - sorry 'bout the brief side-tracking - now back to the original question...
While not being an ARMER listener, I do find that some "smaller" groupings are best - but that seems to mean different things depending upon the system. For example, county or regional systems tend to group things into "fire/ems", "Police", "public works", etc. However, many statewide systems just lump everything into one giant "group" for each county (police, fire, etc.) -- it sure would be nice to make this a bit more consistent across the board (all systems).
In at least one statewide instance, I had to convince the local dbAdmin that although one (super) large grouping was technical valid (i.e. "Department of Transportation"), that top level state department actually consisted of many sub-departments and it made sense to break them up into separate groups. That is - one "group" of talkgroups had at least 100 talkgroups while at the same time, there were smaller agencies that had as few as 1 or 2 talkgroups.
Regardless of radio/scanner vendor, creating smaller, more specific "groups" of talkgroups makes it much easier for users to select what they want to hear vs. having to import lots of stuff and then manual break these groups down into smaller sub-parts (and then having to manually maintain that parsing of the data).
