Core exercises are the basic movements that you should do when you first start bodybuilding, if your goal is to put on size. Bench press, squat, deadlist are some basic core excersises that will help you develope a base before sculpting your body. If your goal is to build up a good fame to sculpt then these are what you should include in your workouts.
Whenever you work a muscle there are individual muscles in each bodypart. Lets take the leg, you have the ham, glut, quad. If your working out your legs assuming you want to add mass on all these muscles you should do excersises that target each muscle. For glutes switch up deadlifts with lunges, hacksquat, hipslead. Then you should hit up the hams. Depending on your gym there should be at least 2 machines or cable you can use. So what i'm saying is don't leave out any of the muscles so that none of them will fall behind. If you can't do all in one day slpit it up for leags twice a week.If your only doing specific exercises that mainly hit the quad then of course the glutes and hams are gonna get weak and possibly lag.
---PEACE---Mad Max