Sometimes Including Independent Variables in a Regression Serve as a "Data

Sometimes including independent variables in a regression serve as a "data sanity check," in so much as they facilitate a:

A) more efficient estimate of the treatment effect in question.
B) more unbiased estimate of the treatment effect
C) comparison between the estimated coefficient for that variable and the value for that coefficient as predicted by theory.
D) secondary measure of the standard error of the treatment effect of interest.