There are a lot of reasons to hit those shoulders hard when you can. The benefits range from strictly superficial to increased overall strength as well as greater function and mobility.
First and foremost big shoulders look awesome, let’s admit it.
The shoulder region is made up of two main muscle groups: the trapezius (traps) which are located at the top near your neck and the main muscle is the deltoid that wraps around from the front all the way to the back of the shoulder. When it comes to basic aesthetics, having giant traps reaching from just below your ears to the ends of your shoulders is just one very cool and intimidating way to set the right tone at the top of your physique.
You can definitely broaden the rest of your shape by increasing the girth of your upper body if you can get your deltoids bigger than Samus Aran’s in her space suit (Nintendo’s Metroid reference). As a man, the most attractive thing you can do, and science has proven this, is sculpt your body outline into the coveted V-shape pattern from your shoulders to your hips. The broader your shoulders, the easier it is to create that illustrious V-form.
There is a lot of strength that comes from the shoulders. Sure, everyone loves to get their chests nice and engorged by benching hundreds of pounds but really you need strong shoulders to push that weight up and complement those pecs. Having strong shoulders goes a long way in assisting the rest of your body in getting through most upper body exercises.
When you are plateauing you may think the key is to hit that muscle harder and more often but it may be an indicator that you have neglected other areas of your body too much. Your tris and pecs can grow and grow by doing isolation exercises but you could still be frustrated eventually by diminishing returns on bench. Toughening up your shoulders with complex exercises like overhead press and even incline bench can really go a long way in improving your performance in other areas in terms of overall strength.
Ask virtually any serious lifter and they have at some point experienced a form of shoulder injury, usually to their rotator cuff, in their lifetime. This goes back to the strength principle above. It is important that a lifter not neglect the muscles that bind his arms to his torso. Many young lifters when they start out are all about the glory lifts, primarily hitting some asinine bench press max, and can land themselves on IR for a couple months that way. There’s no shame in it, most of us have been there before by trying to get that one more heavy rep or add those ten extra pounds to our max. When we hop off the bench press we flex our chest and tris but the poor shoulders go mostly unthanked for their contribution- keeping your arms from popping off like a Mr. Potato Head.
When loading up for heavy upper body lifts it is always going to take some toll on the shoulders and your rotator cuff. This is true anytime you use your arms. This goes for shrugs, press, and especially cleans, where there is a lot of shoulder movement and swinging. Taking time to strengthen your stabilizers and the muscles in your shoulders helps to prevent injury when you are going for those extra heavy upper body lifts.