These look like Sergeant's Spontoons. In theory they could still be used defensively against cavalry charges, as pikes were in the hands of troops in the 17th c. and earlier. But in the 18th c. most soldiers were given muskets with bayonets, and only sergeants had these, and they were both a mark of authority and a tool. They used them to dress the lines: holding them horizontally behind the troops to keep them from straggling, like the sergeant in this painting from the battle of Fontenoy - (scroll down about half way to the detail)- or poking them if they held back. If they felt like, you know, drifting away from the bullets.

It was not just a matter of looking trim: a straggling line of troops could not defend or attack as well as a dressed one, and a dressed line maneuvered better as well.