In what way could LDL cholesterol be important or even vital for the body?

Cholesterol Not LDL. As de. Nguyen indicated, cholesterol, a fat molecule, is made by every animal cell & ~30% of fat molecules in all membranes, makes membranes stronger & pliable. Ldl is a lipoprotein (protein which transports all fat molecules in the water outside cells). People can live quite well, indeed are far more likely to have long lives, with very low LDL concentrations. Ldl always in nmol/l, best <700.
Cellular survival. Cholesterol, including ldl, is needed to make up the cell-membrane, keeping it flexible/alive. Cholesterol is also needed to make sex hormones, among many other substances in the body. So, we do need cholesterol for our body cells to live--all cells. Thus, without it, we won't be blogging. Too much is a bad thing, so keep cholesterol to <200 if you can. Consult your doc. Good luck.