In BOS when flying on JB there are two security lines to check ID's...one for the economy passengers and one for the "even more room" passengers (called "even more speed" security but it only pertains to document checking). Obviously the latter is shorter...but...after that if you do not have pre-check on your boarding pass you still go through the regular scanner (laptops out etc) pre-check goes to the right and has expedited screening.

So...you can pay for extra room and not have TSA pre-check on your boarding pass

As was mentioned the airlines do not choose who gets TSA pre-check (different from the ID/boarding pass check point)