I think the hope is that the 3rd party will allow it to be unlocked early. For whatever reason, such as being able to use a second number on T-Mobile, or overseas travel with local SIM.
And historically, I don't think 3rd party services work all that often. At one time, some reportedly paid carrier employees (like an ATT employee) to put in an unlock request to Apple. I think the carriers cracked down on that. Or the 3rd party unlockers would just put in requests that you could have done on your own anyway.