apache ServerRoot change

In moving from Jaguar to Panther I see that ServerRoot has changed in 
httpd.conf from "/Library/WebServer" to "/usr".

My webserver files are all under /Library/WebServer/Documents and I know 
there is a separate DocumentRoot setting for that.

I'm not sure what the significance of ServerRoot is. I tried changing it 
from /usr to /Library/WebServer and apache wouldn't start with an error of 
"Cannot load ... mod_log_config.so ... (reason unknown)"

I am looking at the apache config because my JC app fails with Panther when 
used via apache / WO adapter - but is ok when used via direct connect.

Thanks
John