Chatting to an ex-Lockheed L-1011 test FE, part of the reason for installing DLC on the L-1011 was it was fairly pitch unstable at landing flaps 33 and 42 ( if my mem serves me...?), so they wanted a smoother vertical rate control for auto-lands. If you look at the plan view of the a/c, you'll see that the tailplane/trailing edge of the wing are very close coupled.
I preferred landing it with the DLC un-latched, personally. Just to add to the tech description, the spoilers also operated in the roll mode through mixers, at the same time as operating in the DLC mode, leading to every check-airmans' favourite question:
" you're high on the approach into HKG and need to tighten, what happens to the positions of all the spoilers during the manouvre? Which hyd systems are powering which? What's their max deflection? 40 or 60, plus or minus the 14 degrees ?" Oh my God....I could have killed that flt-test FE, personally.....
The 747 is much nicer....but the TriMotor was well ahead of it's time, and built well.