Pros and Cons of each Healer Role

[HPDelron]

That sounds like a massive waste of cards and cool downs.

Short: Yes, with a but.
Long Answer: No, with an If.

In 4-Man content an extension gives you double the normal effect on a card, while an expansion gives you half the effect on 4 people.. or double the effect if you will. However since not all 4 party members are equally good in terms of output you get the most value from an extension on the party member most able to make use of it.

In 8-Man content this is much harder to justify, since you effectively get 4 Cards worth of value out of expansion. However if what's gating you isn't DPS there may be value to be had from concentrating other cards a bit more. For example you can imagine content with a lot of scripted damage and small DPS windows where you get gated on healing longevity and so concentrated ewers are going to be the best use of CDs. Also if you've got an extreme setup, say.. 2x Paladin Tank and no room for Healers to DPS and 2-3 DPS that are way more component than other(s) the value may be there as well. Granted these all represent narrow edge cases that I can't imagine come up much, but it's at least worth remembering from a conceptual standpoint.