The Social Knight is a horse mounted unit capable of using either swords or spears as their weapons. While they they do not possess high strength, health or defense, these characters can move very long distances across the battlefield, riding quickly from one area to another. In later titles of Fire Emblem, the introducing of the weapon triangle made these characters much more versatile in fighting different types of foes. Utilizing their ability to use both the sword and spear gave them no real weakness against when facing any type of melee fighter in battle.
As with all mounted units, the Social Knight is able to traverse the map very quickly. Using this ability is often helpful to assist other characters at a far distance, meet certain objectives or quickly block an enemy advance. They also make excellent rescuers once the rescue command was added into the game, able to move far distances, pick up injured allies, and move them to safety. The rescue command also allowed one to move slower units, into battle at a much quicker pace. Due to their average combat abilities, it isn't recommended to fight foes of similar or greater strength. Overall, these knights make strong support characters for other classes.
The Social Knight is eventually promoted into a Paladin after reaching the proper requirements. While their stats are boosted, the largest newfound advantage is the increase of movement, increasing the already large area the Social Knight could already cover in one turn. While this upgrade is useful, especially in terms of support (mentioned above) Paladins should still be treated as Social Knights.