This is good question. When you open an excel sheet, it perform all the excel sheet calculations in order to update the values in the cells. The more calculations you have the slower your sheet will perform. Accordingly, since we have very long formula in the excel sheet which converting rows to columns, and this formula is applied to around 7000 rows, and we do not need to update the data once we put it in place, so i advised you to select all the data, right click and copy, then past the values only (which i referred as 123) This will make the excel sheet perform way faster.
Hope my answer was clear for you.