Assuming you have a list of product names in a column, say one hundred rows. You want to find out how many unique items are there in the list. To do that you can use the following formula:
The second formula is longer but will return the results faster. According to one web site, it is 4-5 times faster. If this is a simple worksheet, you may not feel the difference. However, if yoiu have a complicated worksheet with multiple formulas, the second one may prove to be a time saver if it really calculates 4-5 times faster.