I can give an answer for the economic usage, focused on high middle ages france : In short, not that much. Roman roads were built for armies, and were not adapted to the transportation of merchandise, principally due to slopes that were sometimes too steep for heavy carriages. Fluvial transport was the core of economic transportation, and people resorted to terrestrial transport only if there were no other choices, typically between two rivers.

Source : L'économie médiévale, Philippe Contamine, Marc Bompaire, Stéphane Lebecq, Jean-Luc Sarrazin