The CPU load depends on the length of time a server spends executing a script every time a visitor opens a webpage on a given script-driven site. Static HTML websites use barely any CPU time, but it's not the case with the considerably more sophisticated and functional scripts, which use a database and display dynamic content. The more clients open this kind of an Internet site, the more load shall be produced on the web server and if the database is very large, the MySQL server shall be loaded also. A good example of what may cause high load is a web-based store with a huge number of products. If it's popular, plenty of people will be exploring it simultaneously and if they seek out items, the whole database which contains all of the products shall also be frequently accessed by the script, which will result in high load. In this light, having CPU and MySQL load statistics will give you an idea of how the site is doing, if it needs to be optimized or if you just need a more powerful hosting solution - if the website is really popular and the existing setup cannot handle the load.