Subaccounts are great for analysing GL better and can be super powerful.
Subaccounts for business divisions or areas, or even sales people (a way to do salespersons budgets) is mostly utilized. You can use Unit sets in GL reports to expand subaccounts easily.
They invaribly can be used on any GL account, so if that is the case use subaccounts, but otherwise if a particular area of the GL is only in one area like say Fuel costs, use an account class to summate and different GL accounts for the different say staff members rather than subaccounts.
Keep them simple, and try not to complicate it, as clients can find it difficult.
The automatic combination of them can also be powerful, but to limit mistakes you can set it for this not to happen, but then customer must maintain all their combinations manually that they might require.