Today I helped a customer use the Shred feature of Drive Genius 3 to securely erase a folder on his MacBook Pro that contained documents with his personal information. He was wondering if he should move the folder to his trash, empty his trash, and then run a Shred on the free space. This is definitely one way that he could do it, but I suggested that he should instead go into Shred in Drive Genius 3 and choose the specific folder that he wanted to securely erase.
By choosing to only shred the folder this would save him a lot of time compared to shredding all of the free space on his drive which amounted to around 400 GB. He decided to run a 3 Pass Shred for the folder and he was able to securely erase all of the documents in a few minutes rather than waiting a few hours to shred his entire free space. He was glad that these files were permanently gone and thought it was very convenient to have the option to choose a specific file or folder for the Shred.