When I open in-game options (via ‘Esc’-key) under the ‘Reset Settings’ tab there is an option to ‘Clear All Cache Files’…was going to use it to clear out hard-drive space, but will it delete things like in-game bookmarks, contact lists, etc.?
It deletes static data downloaded from the server - it’s harmless but things like character thumbnails will be black until they are downloaded from the server again. Flushing the cache is one of the first troubleshooting steps to take if the client is misbehaving since the cache can get out of sync with the server. Edit: any saving will be temporary since the client will immediately start saving static data there again - it does significantly reduce bandwidth when you have tens of thousands of active connections.