Most all modern cars have them. When the engine mounts all started going to non conductive bushing and other assorted non conductive hookups the "engine metal" lost its circuit to negative and ground.
Therefore ye ole ground strap was needed. in theory they can be anywhere from engine clean metal to frame, body clean metal.
Most put them behind the engine to cab body to get them out of the way. Braided strap (used for flex and less likely to break when moved) or even copper wire will work(which i use because it more more like original wiring);
Do you need them ? Well only if you have mounts and other items that are allowing the engine to not have a very good circuit. But it sure does not hurt to have them.
If your going for a true restoration and where they go then consult the manuals or ask some of the true restoration guys.
