If you change out your springs, you should reset the oil quantity. I say quantity because the showa twin chamber oil level isn't set by height like most others. You are bound to loose some fluid, and the big question then becomes "how much?"
After you get used to doing them, they are actually faster than measuring the oil height. Just get an accurate measuring container to add oil. A plastic graduated cylinder is definately worth the money. Be sure to let all oil drain out of the forks and also blow excess oil out of the area by the top cap.