It probably would have changed the Battle of Gettysburg from a Major Battle to a skirmish. If Buford had failed to hold off the Confederates at Gettysburg long enough for the Infantry to arrive, then Meade would probably have formed up his army along the Pipe Creek Line. Perhaps Buford could have fallen back and drawn the Confederates with him to the Pipe Creek Line and insured that Lee attacked the AOP there. In any case, the Pipe Creek Line has been said to have been even stronger than the Culps Hill/Cemetery Ridge/LRT line held by the Union at Gettysburg, if so, and if Lee attacked Meade there, the Confederate losses may have been even greater.
Bill N-T

I agree with Bill...if Buford had been beaten back or if Ewell had taken East Cemetery Hill Meade would have fallen back to the Pipe Creek Line. This was a much stronger position than Gettysburg and if Lee had attacked(which I don't think possible) the Union would have won the battle of Taneytown.

newyawk

I have to agree as well. Buford's intention and instructions were not to "beat" anyone. The front-line cavalry's intention was simply to feel out, engage, and delay the enemy, then cover for the infantry. Buford would never let himself be "beaten" unless by some grave mistake. 1/4 of the men were holding the horses for a quick flight in case of a rout by Confederate infantry. This was the reason for the "disguise" - Heth thought he was up against infantry, the numbers of which he didn't know. Knoxlyn (Whistler's) Ridge was held by only several dozen troopers, dismounted, with their horses held behind the summit so the enemy could not see them. It took a couple hours for Heth to even find out what he was against.
I agree also with the theories about Buford getting pushed out - if they had failed in their job to delay the enemy until the infantry could arrive, Meade likely would have fallen back to his original plans and Gettysburg would be known as one of the 10,000 skirmishes of the War. And there'd have been no Tower!
J.D.