Is vitamin K2 important to take with vitamin D3 supplements?

Yes, because vitamin K2 is an important nutrient that helps facilitate calcium that is absorbed in the intestine into appropriate tissues and away from ones that can cause harm. Beneficial tissues where calcium needs deposited for good health includes the bones and teeth. If it ends up in the wrong tissues, detrimental health impairments can occur including the eyes (cataracts), the blood vessels (calcification of arteries), the kidneys (kidney stones), etc.