lammert - 5:12 pm on Aug 12, 2011 (gmt 0)
These processes are started when there is work to do like processing a page or PHP script for example, but in many Apache configurations these processes stay idle for a number of seconds to wait for a next request from the same client. During this period these processes are not able to process requests from other clients and just take up memory and process table space. With te setting "KeepAlive Off" every process stops listening to an existing client as soon as a request has been processed and becomes therefore available to process other requests. This will in general lower the amount of concurrent processes significantly, but the page loa time for each individual client may increase somewhat because for every new request of a page (CSS file, JS files, images etc) a new connection between the client and server has to be established.