I don't think it changes your knowledge or performance. It's just a matter taking shortcuts or a different route to get to the same place.
Raid Rx: Is addon-less healing possible?:
Every week, Raid Rx will help you quarterback your healers to victory! Your host is Matt Low, the grand pooh-bah of World of Matticus and a founder of No Stock UI, a WoW blog for all things UI-, macro- and addon-related.
I see a fair number of emails and messages about this topic. Is it possible to heal without using any addons of any sort? Naturally, the default user interface (or UI) includes a limited number of features where this is possible. Is it recommended in dungeons or raid instances? No, not quite. I've seen opinions from some players where they practically insist that healing without addons should be the way to go. Anyone who does use addons is relying on a crutch. I don't think that's quite fair to say. It's not like these addons are scripts or anything that can 'think' and heal for you.