Face milling, like plain milling, produces flat and smooth surfaces on the workpiece. The difference is in the tool orientation. The cutting tool in face milling is perpendicular to the cutting surface, which means that the bulk of the cutting action happens at the face of the cutting tool rather than its side edges.
This makes face milling an ideal operation for achieving fine surface qualities and high dimensional accuracy. Due to the tool axis being perpendicular to the cutting plane, it is less susceptible to geometric deviations and tool vibrations, leading to high workpiece parallelism.