Using TGT in the cruise to control thrust allows you to gain maximum thrust, as you can run all four engines at max continuous thrust.
TMS could be used to control engine thrust in three main ways: matching TGTs, matching N1s and matching N2s. Most of the time we would match N1; with all four fans running at the same speed, cabin noise was reduced. Theoretically, at higher levels N2 matching would be better for achieving low cabin noise- however, in practice N1 was almost always used instead.
My preferred TMS mode in the cruise was a combination mode, where one selected the TGT on the "master" engine, and the other 3 then matched their N1s to it. This kept the cabin noise to a minimum, but allowed thrust changes to be done using the thumbwheel of the TMS TGT controller.
Airbrakes could be used on the ILS in 2 ways. If asked by ATC, the aircraft could be kept at very high speeds till late on the approach (my personal best was 190 knots to 3 miles) then the airbrakes used to decelerate very rapidly indeed, and still achieve a stabilised approach by 500 feet. On a normal approach, however, airbrakes would be opened after decision altitude (usually between the airfield boundary and the threshold) to reduce speed from Vapp (usually Vref +5) to touchdown speed (usually Vref-7 or so).
Unfortunately I can't remember how we set the TMS for departure- it's been a long time, and I don't have my 146 manuals to hand...