Playing a holy paladin is a lot like participating in illegal street racing. We drive as fast as possible, have no respect for law or our fellow man, and we live our lives a quarter mile at a time. Well, at least the last part is true. We play our class one second at a time, with only a moment's time to process our raid's status before making our next move. We play in a GCD-capped environment: limited by the game's own internal pacing instead of our mana.
It's because we're already capable of casting as fast as possible that our multi-target healing suffers. Most other healers can increase their number of spells cast per second to boost their healing output, whereas we're limited by the fact that we can really only heal one person per second. There are some tricks we can use to beating this GCD limit, and therefore raise our output over simply mashing Holy Light for five minutes a time. Knowing how to work efficiently in these short, one-second windows will ensure you're healing every last bit possible.