At one handred more time I had to reenter cell edit and finally decided to make this message. I and you cannot move cursor to some already typed letter with usual left arrow key while entering data for blank cell - Excel decide that you finished with this cell and select RC[-1] cell. You have to press right arrow key and F2 to continue with needed cell. This is annoying.
You don't have this problem if you edit cell which already had some data b4 editing.
I don't think that moving to RC[-1] cell with left arrow give some speed up for data entering from the scratch. Do you? If you don't, please, consider this message as a bug report :)