Yeah, it will lower some of your stats, consequentially if you are relying on stats given by that shield to wield another piece of armor, a weapon, use certain skills (whether bound to the shield itself or unlocked as an enchantment effect on it), then you will lose access to those as well. For example, wielding a shield that has +1 Pyro, and then utilizing that as a way to equip fire spells without having invested natural points, if you were to lose access to the shield, those spells would be unslotted out of memorization (even if you were to somehow increase or restore your con, you wouldn't be able to use those spells as they were unslotted after you lost access to them; you can't slot spells you don't have the skills for).
So be very careful with the Flesh Sacrifice, pumping a few points in may not be the worst idea ever, though it certainly has it's risks.
