mod_proxy_ajp or mod_proxy_http?

[Bill Stoddard]

I'm trying to understand why mod_proxy_ajp exists and what it provides 
that mod_proxy_http doesn't.

ajp13 is a binary protocol which should make the ajp13 tomcat connector 
a bit more efficient than the http11 connector; an incremental 
performance improvement. obtained at the expense of added complexity. 
Does mod_proxy_ajp provide any other function not available in 
mod_proxy_http? I'm trying to decide which horse to put my chips on :-)

Thanks,
Bill