Quote:
At the expense of wasting memory, sure. mod_php will load PHP into every single Apache process even if they're serving up static content.
It's important to look at a site's actual requirements and understand the tuning options available in Apache before deciding to throw mod_php out over something like this. Many high traffic sites use it without any issues, and the actual traffic expected on a site should be taken into consideration, with load testing, before making such a call.
If optimizing the memory footprint and overall performance is critical, it's always possible to offload static content to something else, such as nginx or another web server daemon, without having to use it for everything. This has also been a common practice for high traffic sites.
Edit/addition:
For sites with very high traffic, it is often highly desirable that they be hosted on more than one web server for traffic management and redundancy purposes. One method of accomplishing this is discussed here:
Build a Highly Available HTTP Load Balancer on Ubuntu 10.04 LTS (Lucid)