Again...when the cartilage around the rib's, etc is still in a elastic state, and has not reach a more mature stage, than the possibility of enlarging the rib box's can happen. The mean average in humans is between 22 to 24 years, or abouts, before the cartilage starts to become set or firm. Pullover's have helped increased the depth & width of many men (and women) over the years. Approaching this exercise with serious intent, while the cartilage is still in a state of flux, could product rib box gains of 2 to 4 four inches after a period.. Think of having a 45" muscular chest and than adding 3"s, through expansion of the rib box, for an impressive 48 inch chest. Even if one is in their 30's-40's+, doing regular set's of pullovers seem to influence the lifting of the muscle attachments around and supporting the chest/rib box, giving more flexability and a fuller feeling to the chest overall. All are great for improveing the full lat sweep when the arm's are held overhead, double bicep pose, front/back lat pose, etc.
Pullovers, either straight or bent-arm, is a great growing exercise for the lat's, pec's & triceps. Also hits the abs strongly. Adding the press at the finish of the bent-arm pullover (Pullover & Press) only increases the value of this main upper body mass producer. DB's or BB's each work well but the DB's seen to lessen any stress on my elbows & wrist. Doing pullovers after heavy deep breathing producing movements, like squats, DL's, cleans only add to the advantage of expanding the rib box. Good Luck.