Humans are built for forward moving activities, we walk forward way more than we walk backwards, sometimes people don’t walk in reverse at all. Along with this we also like to move objects forward that are in front of us, we love to push.
You walk into any gym right this moment and I can guarantee you will see someone performing some sort of bench press, whether it's barbell, dumbbell, push up, or some machine variation of a horizontal press. The horizontal press activates the muscles of the anterior rib cage, the pectoralis major and minor, the serratus anterior, the deltoids and the triceps to move an object away from the chest. (Rhomboids, lats and other smaller muscles are also activated to stabilize the scapula and the position of the back) Looking at the bench press the weight is lowered down towards the chest, as that occurs the pecs are lengthening, the glenohumeral joints are abducting horizontally then the elbows bend, lengthening the triceps as we go into the concentric portion of the lift it is the reverse, the pecs shorten with horizontal adduction the triceps shorten and extend the arms to a full reach position.
Horizontal pressing should be part of all strength training programs to develop optimal strength through the upper body, but it can go too far. Too much horizontal pressing can influence body posture and lead to a shortened state of the muscles thus pulling the shoulders forward and giving a rounded shoulder posture. (Winged scapula or kyphotic upper back) To make sure that we do not create postural imbalance we need to strengthen and perform the opposite movement, horizontal pull. A good rule of thumb we use is if you are performing a chest press of some sort in a workout, there needs to be a horizontal pull exercise somewhere else in the day. If not it's not the end of the world, we want to train the brain to acknowledge positions and know that it can perform a movement in one position but it can come out of that position to a neutral state. Performing the horizontal pull will keep the systems in balance.
Looking to get stronger? Check out the Wendler 5-3-1 program. Read more about it here