Here is a interesting article from Joseph Cox on encryption in the home and how well it stands up. Despite no sources being listed it gives what I consider a comprehensive look at the problem at hand of layering your encryption.
“This way, if you are stopped and forced to decrypt your hard-drive, your adversary is going to only have access to what you have deliberately stored on that computer. If your PGP secret key is stashed at home, or the leak you were provided with is on a computer elsewhere, your adversary isn’t going to get hold of them. But if you didn’t take this precaution, they are likely to gain access to everything: articles in progress, notes, interview transcripts, the lot.”