Roller brushes dig into carpet while side brushes sweep edges — they do different jobs

The roller brush is the main spinning cylinder underneath — it agitates dirt from carpets and hard floors so the vacuum can actually suck it up. The side brush is a smaller spinning arm on the edge that sweeps debris from corners and baseboards toward the roller brush. They work as a team: the side brush pushes the mess into the path of the roller brush, which then kicks it into the suction channel. Without the side brush, corners would accumulate dust bunnies. Without the roller brush, you’d just be pushing air around on carpet. You really need both for proper coverage.