Healers have one of the more ambiguous roles in the World of Warcraft. DPS players mostly thrive by topping the damage meters, using the most optimal rotations, glyphs, etc. Tanks enjoy a form of tunnel vision where their task is ever so straightforward and clear. A healer, however, must keep watch on a whole group of individuals, react to their choices and keep the game itself from defeating them.
The worst kind of healer will select one, two or possibly three go-to spells to spam often and early. This player will use healing meters as a measure of success and frequently use them to lay the blame on others when things don't work out. The best kind of healer uses a wide array of abilities at exactly the time required. He conserves mana, keeps everyone alive and even contributes to the raid's overall DPS when possible. The best kind of healer isn't simply the reason you lived; rather, they're the reason things went smoothly.
Many healers rely on mods as they strive for this goal. Healbot, for example, creates a special frame for click-casting. It assigns certain spells to certain mouse buttons by default, making healing a breeze. The chief limitation of Healbot, however, is the link to physical buttons on a mouse and the lack of native support for more than five of them. Without keyboard mods, a Healbot healer is restricted to no more than five heals that are ready at a moment's notice. This player will also need a fair bit of practice to get beyond the defaults of "left click, little heal; right click, big heal." Memory plays a role, as Healbot does little to notify you visually of which keys do which action, especially once you've sized the bars down to the point that you can view the entire raid.