Depends on the block. Open decks with non siamesed cylinders need a torque plate to stabilize the cylinders during boring/honing. With siamesed cylinders+open deck you can get away without a plate, I wouldn't, but you can.
Regular closed deck blocks always need a torque plate.
IMHO any aluminum block needs to be finished with torque plates as well as every loaded fastener that goes into the block present and torqued to spec.