There was a time when I thought that encrypting my entire harddrive and then encrypting a folder was a stupid thing to do. The compression experts have made it clear that double compression does not work so I was already biased.
Encrypting the entire harddrive makes perfect sense because with few or any exceptions the harddrive is linked to the CPU an therefore cannot be removed from the computer and connected to a USB without a lot of low-level knowledge… even is at all possible.
And so for the most part, most operating systems, are not likely to leak any confidential data into the swap or sleep partitions as non- encrypted systems commonly do.
But the advantage of encrypting a folder with “Espionage” or “DocWallet” has the added benefit that your sysadmin and the people you share your computer with are not likely to be able to access these doubly encrypted folders.
As a side note… If your concerned about PRISM-like attempts to hack your data then I have no idea if this is the right vector. There are so many ways to gain access to personal data in a computer, from a hackers perspective, that all of these methods are just providing a false sense of security.