I was about to say, "In particular, it might be helpful for debugging settings to remain in the config file. Suppose you install an experimental extension that crashes the wiki. To fix it, you have to comment out the require_once line that installs the extension, then go to the config screen to change the debugging settings, then re-enable the extension. This is a three-step process which under the current setup only takes one step." However, it seems to me that on test wikis (as opposed to production wikis), people will typically keep the debugging settings switched on.
