In the 1930s KLM bought a single Stearman-Hammond Y so that the pilots could learn how to take off and land an aircraft with a third wheel at the front. Up until that time, taildraggers were the norm and with these, your wings have a positive angle of attack from the start of the take off run. As elevators become effective long before lift off speed, and as the unprepared surfaces of those days could be troublesome for nose gear legs, the practice of lifting the nose wheel and letting the aircraft fly itself off came about. There are some drawbacks though:
- You will be lifting off at the minimum flying speed, making every speed excursion within those first minutes hazardous. One little gust could ruin your day.
- As there is a lot of variation possible in attitude, the take off distance needed would vary a lot from take off to take off.
- Lifting the nose too high could leave you in a stalled attitude on the ground (as the Comet would show in its early days).
As a result of this, the concept of rotation at a pre-determined speed was developed. This technique led to a lot more precision in calculating needed runway lengths and allowed a margin of speed over the stall speed at lift off. It also helps with directional control during crosswind situations as mentioned above.
An interesting side effect is that we now see private pilots on Cessnas and Pipers who will tell you that their trusty steed has a 'rotation speed'. On a light GA type, I feel that the 'lift the nose early' technique is still the best way to take off, and that a rotation speed is absolute nonsense, but it's difficult to get this message across when every Cessna pilot thinks he's a Boeing pilot in training. But that's a different discussion....