What are the uses of Lugs/Ferrules?
1) It's not easy to make a safe and reliable connection under a screw head to stranded wire, especially wire with hundreds of strands (like very flexible very large gauge wire). The barrel of a lug is designed to keep all the wire strands safely contained and under control. This is especially true where solder is an unreliable mechanical bond for the wire to the equipment (e.g. in power distribution systems)

2) If the wire needs to be removed, replaced, moved, or added to the device, then a lug and lug socket (or screw/bolt) is a more field-configurable type of connection, and can be mated/unmated many more times than bare (especially stranded) copper wire.