A TMS and an accounting package overlap at the edges but are built for different jobs. The TMS knows about loads, lanes, drivers, accessorials, and PODs. The accounting system knows about the chart of accounts, tax categories, payroll, and the P&L your accountant needs.
A very small operation can lean on one and improvise the other — invoice from a TMS and hand a shoebox to an accountant, or run everything through accounting software and track loads on a spreadsheet. Both approaches leak: the first has no clean books, the second has no operational visibility.
The practical setup for most carriers is a TMS for operations that pushes invoices and payments into the accounting system automatically. The integration is the point — without it, every invoice is entered once in the TMS and again in accounting, which is exactly the double-entry a TMS is supposed to remove.
Terms in this answer: Settlement, Chargeback
In Trailflow: accounting and integrations.