Correct technique increases efficiency. And efficiency is important to fitness because it allows you to do more work in less time (the definition of fitness).
Just like any movement, there are correct mechanics to using the indoor rower. Collectively as a gym, we have many poor habits like opening the hip too early or leaning back too far.
Here is the World Rowing Indoor Championships from last year where the men raced for 2,000-meters. Take a look at how efficient these men are as they sprint on the rower.