First: Clones can perform various attacks all at the same time. Indeed, imagine if you had four clones in front of you all release different jutsus at you at the exact moment. Dangerous, no?
Second: It is hard to tell the difference between the real you and clones. Only the Sharingan is able to tell such differences, or normally, people just godmode this in battle.
Third: Being able to combo greatly with split-second jutsus.
Can you think of anymore?