They take memory for sure when loaded, also when greyed out.
Wether they take cpu depends on if they have been initiated in the song or not. If they have not been fed with a source, they may not consume cpu power if the plugin is turned off, however if they were being turned off while processing an audio-feed, they may keep buzzing in the background until suspended by a routine of its own or just keep buzzing because the plug may not have a suspension routine nor does not respond to suspend signals from its host.
In that case they may consume noticable cpu power as well.
For autosuspended plugs this is true, for bypassed plugs not: They do not consume any CPU when bypassed.
Completely autosuspended (silent plugs) are like bypassed plugs. Plugs are never unloaded from memory until you delete them.