Something that's controlled is kept in check or restrained. Your controlled laughter in math class won't get you in trouble, because it's muted and calm.
Some people really blow their stacks when they get angry, while others express a controlled anger, calmly explaining their frustration. The ability to keep your emotions controlled is a useful one. A different meaning of controlled is "restricted by law," — many medications and drugs are classified as "controlled substances. The root of both controlled and control is the Latin contrarotulus, "a register, counter, or record of something."