How many times have you seen a piece of JavaScript or PHP code that’s only purpose is to add a specific class to the first, alternate or last element of a list or row of table? With CSS3 you can easily get rid of all of that logic and replace it clean and simple CSS selectors. This will help tidy up your code and depending on what exactly the code is doing reduce CPU load by removing unnecessary recursions (This is of course a minimal gain, but every little bit counts)