Jeff, locking a component or group makes it so you can't inadvertantly change it. You can't edit it or move it without unlocking it first. It might be a good solution to prevent goofing things up.
FWIW, you can also revert to an earlier saved (manually or auto-saved) version. Depending how much you've changed the model since the last save, or how long ago you made the error, reverting my help you avoid having to start over.
And finally, if you screw up a component or group, temporarily save the current file using Save as and give it a new name (Entertainment Center b). Open a new session on SU and open the previous version of the file. Copy the component and paste it in the newer version. Use the old version to replace the screwed up version.
Irony: The opposite of Wrinkly