If you came from an Apache environment, you might have set your Virutal Host root dir to /var/www.
By default, this folder is created under the root user.
If you already have websites running under /var/www or other locations you can leave it like it is. For me, I like to run it under my home dir so I don't have to worry about permissions set by root.
One of the nice thing about experimenting with new stuff is that you can do whatever you want :)