Throttle lock?
Are you referring to the ~1/2 throttle lock used for cold starts?
I've seen the lock switch integrated into the off switch. Middle will be normal running position, down will be 'off' and up will be the throttle lock.
If this is what you're talking about, then it's not very usable. First, it only locks at partial throttle. Second, it un-clicks when applying more throttle.
So, besides cold starts, the only thing it's good for would be low power trimming, but I don't see how that's very helpful.