If you add the ELSE-statement to a rule, it means that for every item that is not collected in the IF-statement, the action in the ELSE-statement will be used. Due to this functionality, the ELSE statement will decrease the number of rules you need to create. For example, the image below displays the way "availability" can be filled in using this statement. Previously, you needed to create two separate rules, one to fill in the value 'in stock' and one to fill in the value 'out of stock', but with the ELSE-statement you only need one rule.
If stock is greater than 0,
Then take availability and set to value "in stock"
Else take availability and set to value "out of stock"
If saleprice is greater than 50
Then take shipping_price and set to value "0"
Else take shipping_price and set to value "3.95"