In the gym we're constantly trying to get athletes to maintain good positions, whether it be during weightlifting, bodyweight movements, or even mono-structural conditioning elements (running, rowing, jumping, etc). The cues you hear of "chest up" or "chest out" or "set yourself big and proud" are really just tools we use to get athletes in better positions to move external objects or their own body through space. And really, posture is just a proper-sounding word for position.
Good posture in the gym hopefully leads to an increased awareness around better general posture in one's daily life outside of the gym. The folks at TedEd made this little video about the benefits of good posture - check it out:
WOD for 02-14-17:
Alternating EMOM For 4 Rounds (12 Minutes):
1) 15/12 Calorie Row
2) 7-5-3-3 Deadlifts, climbing to your working weight
3) 200m Run
Treat this as an extended warm-up, not as a conditioning piece - thus the easy target numbers on the row. Deadlifts should climb in weight up to (or just past) your working weight for the workout below, and the run should be a brisk stride.
5 Rounds For Time:
20 Box Jumps @ 24/20 in
15 Wall Balls @ 20/14 lbs to 10/9 ft
10 Deadlifts @ 245/175 lbs