The CPU load depends upon the amount of time a web server spends executing a script each time a visitor opens a page on a certain script-driven website. Static HTML sites use barely any CPU time, but it's not so with the significantly more complex and functional scripts, which use a database and display dynamic content. The more customers open this sort of a website, the more load shall be generated on the hosting server and if the database is large, the MySQL server will be loaded as well. An example of what could cause high load is a web-based store with tens of thousands of products. If it's popular, plenty of people shall be exploring it at the same time and if they look for items, the whole database that contains all the products will also be frequently accessed by the script, resulting in high load. In this light, having CPU and MySQL load data will give you an idea of how the site is doing, if it has to be optimized or if you simply just need a more efficient web hosting solution - if the site is extremely popular and the established setup can't handle the load.