If you make a fake key, then you can walk in with people all around without looking suspicious. You can even act like the owner whilst in a group of non-conspirators. Even with a great picking kit, it's going to look different to anyone looking somewhat closely.
Depending on the level of physical security surrounding the lock itself, this difference could be as extreme as the difference between knowing the password and having a great rainbow table. In the former case, you can log in as the owner without arousing any suspicion. In the latter case, you have to have some time when nobody is looking (download the hashed password database).
So get a big bright "ABC Locksmithing" shirt printed up and carry a toolbox while commiting crimes. Odds are good nobody will notice you then. Or just change the lock and come back later for the theft, now that you have a key.
Depending on the level of physical security surrounding the lock itself, this difference could be as extreme as the difference between knowing the password and having a great rainbow table. In the former case, you can log in as the owner without arousing any suspicion. In the latter case, you have to have some time when nobody is looking (download the hashed password database).