If damage would be dealt to another creature you control, prevent that damage
What that means is that you can load up Shimmer Dragon with 4 sweet pieces of equipment, attack someone, and then tap those swords and boots and whatever to draw 2 cards
But yeah, its ability is nearly useless in a mono-color deck unless you only have your Sol Ring and utility lands left to tap
#22 Mana Crypt - Rogue Reading doesn't just make you smart, it makes you mana
Force of Vigor is one of the many cards free spells which have been printed in the last years, and will remain a staple in sideboards for as long as Affinity, Amulet Titan and Hammer Time remain competitive in the format
A good Liesa deck includes lots of creatures with lifelink, as well as ways to boost your lifegain, like Angel of Vitality and Boon Reflection