From memory, the POH says to use the Low Boost Fuel Pumps in temps above 90 F (32 C).
I queried my chief pilot about it once and he said there is no need to ever use them - even though the temp was usually "about" the 90 F (32 C) mark. I remember he even once pointed to the OAT gauge and said "see, it is NOT above 90F".
Therefore I never switched them ON for take-off/landing and never had any problems. This company had been operating Barons in the tropics for maybe 20 years so I suppose they knew best about how to operate them.
However I once flew in a Baron belonging to a different operator on the airport and I noticed the pilot did switch ON the low boost pumps for take-off / landing. This was on a flight late in the afternoon and I am quite sure the temp. would have been below 90 F at the time.