Manual:$wgMiserMode

Details
If true, disable database-intensive features, so that they can be managed/controlled separately if desired. This includes reading special pages marked as expensive from the cache instead of regenerating them every time they are requested.

With $wgMiserMode set to true, this means that the SpecialPages managed by this flag will only be updated when explicitly made to update. For example, setting up a cron-job to call /maintenance/updateSpecialPages.php or using Extension:RefreshSpecial.

It also disables namespace selection and RevisionDelete selection on Special:Contributions and the like (r88025).

The other disabled features are...