I believe the point is prefork will run "faster" if you have the RAM to support it - many new admins think "oh I've got a quad core I should be good for 1000 clients" and configure their server so, not realizing that for mpm_prefork to support 1000 clients you basically need to be able to fit 1000 copies of Apache in RAM (there's more to it than that, but it simplifies and illustrates the problem). That's why in the first comment on the entry above, you see "my server is overloaded, but CPU usage is low" - because the server is spending all it's time swapping virtual memory and not doing any work.
Note that the comments on that entry Re: PHP5 are outdated. Almost everyone in the intended audience of this site runs suphp, which implies fastcgi, of which mpm-worker is nothing but an advantage. Note that there may still be other Apache modules that aren't thread safe, but most people don't have any problems with it.
If you're using mod_php, you might carefully consider mpm_worker, otherwise I'd say just give it a shot.