'sub location' under 'location details' table and how is this different from 'location groups'

Hello

what is sub location under location details table (shown in below column under location details grid) and how is this different from location groups?

I'm trying to group individual locations together.
I know this can be done via location group; however I would like to have different levels:
such as collection of (testpits, bore holes, DCP locations) in an excavation trench. I have assigned these location group calling Trench01, Trench02, and so on
I would like to group these trenches into areas, such as (locations in Tench01 and Trench02) called Area01, and (locations in Tench03 and Trench04) called Area02, and so on

I have grouped certain 'locations' and 'location groups' using 'phase' or ' location purpose' columns.

However, there is a column named 'Sub Location' which isn't clear what this is used for?

Can anyone shed some light please.