The primary function of most freight trains is to transport goods for paying clients. But to turn a profit, railroads need to pay for things like track and bridge inspections, car scale calibration, derailment cleanup, snow removal, and the feeding and housing of maintenance staff working in outlying areas. Hence, the use of maintenance of way cars.
A model railroader might replicate realistic railway operation by repurposing decommissioned equipment like a real railroad and using HO Scale maintenance of way cars.
Downgraded passenger and freight carriages may pass for HO maintenance of way cars if they’ve undergone some heavy weathering. But adding an HO Scale MoW car to your set from Midwest Model Railroad will give your train a more distinctive look.