If you have 2 columns with 1000 rows each (say column A and B) and you created a formula in the first row (e.g. in column C). In most cases, you would have copied the formula throughout the 1000 rows by dragging the formula down. And one problem you faced is that you would take quite a while to drag to the 1000th row. In addition, you are likely to drag beyond the 1000 rows and have to back track.
Now, there is a simpler way. It just take 2 seconds to copy the formula down 1000 rows, or even 10000 rows. What you have to do is to move your mouse cursor to the bottom right corner of the formula cell in column C until a cross appears. Then double click on your left mouse button. Excel will make reference to the cells to the left of the formula cell (Column B in this case) and copy the formula all the way down to the last row (reference to column B). And you are done.
Enjoy your weekend!