Hi capt. solipsist,
That's strange - because my copy of FCOM says:
FCOM 3.03.11 Page 1
BEFORE TAKEOFF
Pack 1 and 2 … As RQRD
Consider selecting packs OFF, or APU bleed ON.
This will improve performance when using TOGA thrust.
In case of a FLEX takeoff, selecting packs OFF or APU bleed ON will reduce takeoff EGT, and thus reduce maintenance costs.