The question that came to mind was "why didn't Tarleton rest and feed his men prior to the battle?" I know I'm not the first to ask this question, but it strikes me as vitally important.
My first thought was that Tarleton, being a rash glory hound, didn't give thought to, nor care about the physical and mental state of his men. That he was so overconfident in his men that he could push them as hard as possible and still expect them to easily defeat the emeny. Also, he was so eager that he gave little thought to tactics, either his or Morgan's, but simply wanted to rush toward victory and glory..
However, after further research on "Bloody Ban", I have a different view on his actions. I think, given his success at other places, especially Waxhaws, Tarleton thought a straight foward assault gave him the best chance to win. There are some similarities between the two battles. At Waxhaws, Tarleton was chasing an enemy that wasn't looking for an open battle. At Waxhaws, his speed led to them catching the enemy before they had time to prepare properly. Even though it wasn't a surprise attack (he had sent a letter offering to let Buford surrender), Tarleton's speed, and Buford's incompetence, led to him catching the enemy unprepared and vulnerable to a straight forward cavalry charge. So Tarleton's speed and brashness had paid off in the past.
At Cowpens, Tarleton had to believe he had the advantage. After all, he was the one pursuing a fleeing enemy. Perhaps when he heard Morgan was preparing for battle he simply thought they were desperate and had no choice but to fight (this was true). Perhaps he also surmised that his troops were so much better that a quick charge would have the same results as Waxhaws (this was not true).
Another factor could have been psychological. Tarleton probably knew that the only thing that moved faster than his men was his reputation. He may have thought that waiting for his troops to rest and eat breakfast would have been sending the wrong message to his men and his enemy. This could be seen as showing weakness.
Also, this was the largest command he ever had and the first time he was the supreme commander at a large battle. He was didn't have much experience in tactical movements on the battlefield. His tactics were to hit first, hit hard, and overwhelm the enemy.
Of course, it turns out that Tarleton did underestimate his enemy. Morgan wasn't Buford. Morgan took the time to devise a well thought out strategy to counter Tarleton's attack. With the clarity of hindsight, Tarleton would have been better served to take the extra time to rest and feed his men, but he was young, successful and invincible, so caution wasn't a quality he possessed. Besides, it went against his nature. He was a gambler and trusted his luck and ability.
I think Tarleton has gotten too much bad press from American historians. Many of his "atrocities" have been accepted as fact, even though there is little evidence to support them. I think that if you judge him by the standards of the day, and from an unbiased viewpoint, he was no worse than most of his peers. For instance, based on the statistics, "Tarleton's Quarter" is more myth and propaganda than reality, but that is a topic for further discussion.
Tarleton's decision to rush into battle was based on his past successes, his underestimation of his enemy, and his inexperience dealing with a force like the one waiting for him at Cowpens and a leader like Daniel Morgan. I don't think it was just sheer cockiness or stupidity. After all, the battle could (and almost did) go in a very different direction, resulting in a disastrous defeat for the Americans.