Directory Redirect to Subdomain

For the longest time I was redirecting like this

RewriteRule ^(forums.*)$ http://forums.example.com$1 [R=301,L]

without noticing that it’s redirecting to a new subdomain but keeping the directory structure. Essentially redirecting this example to http://forums.example.com/forums/. Which is is bad if you intended to install at the subdomain’s root. It took some reading with the help of Google to realize the proper way is:

RewriteRule ^forums/(.*) http://forums.example.com/$1 [QSA,R=301]