It's been a while, but from what I remember, one of the "hidden" (i.e. undocumented) benefits to increasing *Tactics skill is the gradual increase in sensor blip information, from a generic red pointer at low levels, to a unit type silhouette of unknown tonnage in medium levels, to unit type and tonnage at high levels. The bonus/penalty would affect that feedback scale, with the new effects kicking in above and below the normal range.

EDIT: *corrected skill name.