PunkRockTuba said:
You can use Secure Empty Trash too, when you are ready to empty the trash go to the Finder menu and select "Secure Empty Trash". It might take a little while to delete everything because it has to find all the little files that go with what you are deleting. It doesnt take forever, unless you are deleting a ton of stuff. So if it looks like its stuck, just give it time. Somebody please correct me if im wrong about this.
This is not what is meant by "Secure Empty Trash". When you delete a file (put it in the trash and empty), it is actually still on your hard drive. The OS just removed the 'link' to where it was, the magnetic orientation is still there. As your drive adds new information, it will overwrite the area where your file was. However, given the right applications, you can recover files that have been deleted, but not yet overwritten.
"Secure Empty Trash" not only removes the 'link', but also overwrites the area on the disk where the file was stored with '0's.
Sometimes even files that have been overwritten can sometimes be recovered. If you open Disk Utility, you can click on your HD, and then the 'Erase' tab. Choose "Erase Free Space" and you can overwrite the free space with '0's, either 1, 7, or 35 times for ultimate security.
As to the OP, yes, it will normally leave prefs, etc, but they are very small, and you do not need to worry about them. If you are, try AppZapper, as suggested.