For many people, no it's not. Becuse their metabolism just decreases by the exact same amount they cut calories. They cut out the daily donut, and they find themselves fidgeting less and wearing a sweater because they're suddenly a little chilly a lot of the day. And the scale doesn't budge.
For many people, losing weight is a whole lot more complex than reducing by x calories per day. Getting your body to burn fat rather than slow its metabolism can be maddeningly difficult.