There are three options (that I know of) for automatically enabling a plugin in new sites.
-
Move the plugin from
wp-content/plugins/
towp-content/mu-plugins/
(MU = Must Use). But then it cannot be deactivated for any site. -
Click Network Activate instead of Activate to enable it for all sites. I didn't want to use this though because I didn't want to affect existing sites. Also I couldn't work out how to deactivate it for some sites (although I've read this should be possible).
-
Write a plugin (in
wp-content/mu-plugins/
) with a hook that activates the plugin at creation time. This way it only affects new blogs, can be deactivated easily, and I can also set the default configuration at the same time.