Having now [been able to replace my cigarette lighter](https://mechanics.stackexchange.com/q/36102/1863) on a 1999 Peugeot 206, it's become apparent that it's on an always live fuse rather than an ignition switched one. 

Is this okay or will it drain the battery? Presumably leaving draining components like a sat nav is a bad plan, but how about the USB adapter on its own? Is it safe to just pull all the components out and leave the empty socket?