That's what got me thinking about it, I spent most of Friday sitting at Felts waiting for avionics work and the Medstar chopper(s) [not sure how many they have] were flying a bunch, as was Sheriff One, and I've heard it when they land on hospitals and aprons at GEG and other airports.
I figured it was a required phraseology thing, just wasn't sure of the purpose... but the "area not in sight" explanation makes sense I guess. Hard to clear an area you cannot see I guess.
Area not in sight is what I was referring to in my post. Im in their Class D airspace, but am not landing on their airport. Therefore, they can't really clear me to land, as they can't see where Im landing. They can give me winds/WX and any other advisory info, but they aren't going to formally clear me to land or depart an area they don't control and see.