There should be no part of the body that is a mystery to you. If it’s a mystery, then you won’t be able to draw it accurately without copying it or just making up stuff that doesn’t exist. With knowledge, you can design the body to make changes. You can decide what to exaggerate, what to eliminate, or what to add that’s not noticeable in the reference. When you’re able to change your reference you are no longer a slave to the reference. You can call on it when you need to. You can ask it for inspiration. And you can create your own unique work of art that stays true to your vision and the story you’re trying to tell. When an arm is up in your photo, but you need it to be down to create a better composition, you can do that. When a leg of some figure is too busy with information, you can relax it and show just the major forms. You can show more structure in a figure that you want to feel more solid and heavy.