It depends on which Clear line you go through. The Eastern side (towards gate 1) is frequently very long, for all the lines. In all the times I've been there, I've never seen it less than very busy.
The middle security checkpoint (near gate 12) also has a Clear entrance, and that has always been empty every time I've been there. The Precheck line might be empty, or it might be longer than the regular line -- I've seen both types of situations, on multiple occasions.
The West checkpoint (near gate 27 and above) is one I'm not as familiar with. I don't know if they have a Clear line or a Precheck line. We almost never go through there.
Oh, and the East checkpoint might have separate Clear-only, Precheck-only, Clear+Precheck, and regular. I'm not sure. We don't go down there much.
The middle checkpoint has Clear, Precheck, and regular. There's no fourth line -- if you're in the Clear line, they just take you to the head of whichever other line you're going through.
The middle security checkpoint (near gate 12) also has a Clear entrance, and that has always been empty every time I've been there. The Precheck line might be empty, or it might be longer than the regular line -- I've seen both types of situations, on multiple occasions.
The West checkpoint (near gate 27 and above) is one I'm not as familiar with. I don't know if they have a Clear line or a Precheck line. We almost never go through there.