This plugin disables the custom fields metabox that WordPress includes by default. The custom fields metabox includes a slow query, which on large sites can take 10+ seconds.

Do not install this plugin if you rely on the custom fields metabox. If you do not know what this means you should probably not install this plugin. If you are using a plugin such as Advanced Custom Fields, Custom Field Suite or similar to manage your custom fields don’t worry – these plugins will be unaffected.

The custom fields metabox performance is currently being discussed in Trac. If you find this plugin useful you may want to follow that ticket.