Your core is critically important. Its job is to help create movement (at times) and resist movement at other times. Yes, I get it, people like to just train flexion movements, like crunches, leg raises, situps and what not because that’s what we “think” our core is, but if you are only training spinal flexion you might be really building up the core strength you need. Our core is comprised of more than just our rectus abdominus aka “your six pack” but also obliques, low back muscles, arguably your thoracic muscles, serratus anterior, some of your hip musculature and so…the point is there is a lot more to your core than having a six pack. So yes, people can train those muscles through movement (side bends and what not) but we also need to think about resisting motion. Exercises that train dynamic bracing are awesome for developing stability through the spine. Movements like overhead carries, unilateral farmers carries, pallof presses and so on should all be integral parts of your core training.