VirtualHosts and logs are invaluable features of a web server. However, you may not always want to log things for every VirtualHost. If you simply comment out the logging commands of a VirtualHost, then transfers to and from the VH will be logged to the main (ie, parent) log file; commenting them does not disable logging for a VirtualHost.
If you want to disable logging for a VirtualHost, one option is to log to a file in a temporary directory that gets flushed regularly, but a better solution is instead to have it log to a non-existent file (nul in Windows, /dev/null in *nix/Mac), such as in the following—mixed example—commands:
<VirtualHost …>
…
ErrorLog nul
CustomLog "nul" common
CustomLog dev/nul referer
CustomLog "dev/nul" agent
…
</VirtualHost>