During the main loop in sagbi if no new sagbi generators are added and the AutoSubduceOnPartialCompletion flag is true then all sagbi generators are subducted against each other. This a significant time investment, however if no new sagbi generators are to be added then the subduction of the sagbi generators will speed up the computation of the groebner basis of the reduction ideal and S-pairs.
The object AutoSubduceOnPartialCompletion is a symbol.