Cooperative group play is rather the point of an MMO. If you play an World of Warcraft and play alone, why not fire up a quality single player game instead? But if you play on a sporadic or very limited play schedule--which for the purpose of this post I will call casual--it’s not always easy to find a group. That’s why I argue that healing and tanking are the best roles for casual players who enjoy group play. Healers and tanks have a much easier time finding groups, are usually accorded more respect in groups, and have more flexibility to leave groups that don’t please them.
I Was a Teenage Druid
I started healing at level 12. I went to a battleground and quickly observed that healers were extremely powerful and in short supply. It made sense based on my experience from console RPGs, where I had used parties of multiple healers to defeat boss encounters at low levels, rather than grinding out level-ups or powerful items. I chose healing because healing felt powerful.
One Deadmines run was enough to also show me the social benefits of playing a healing role. I could find groups and run dungeons quite easily. Since I leveled on a low population server before Looking For Dungeon, that was a substantial benefit.
LFD Changed Everything - And Tanks and Healers Still Have It Better
LFD has taken some of the glory away from being a well-known healer (or tank) on the server, but it has given the benefit of finding groups even faster. That's particularly apparent while leveling. If you have an hour to play, and you put yourself in the queue as a tank or healer, chances are you'll get to spend most of that hour running a dungeon. If the dungeon group goes poorly, you'll be able to get into another one easily. If you queue as DPS the wait times are much longer and you're likely to waste as substantial amount of your limited play time sitting around, waiting, or perhaps playing WoW the single-player game.
The drawback of tanking and healing is that even at low levels, you can't phone it in (as much). Your mistakes are more likely to result in a wipe. That can be stressful. On the other hand, since your mistakes make a difference, you're more likely to learn from them. What’s more, you get to feel powerful. Your choices as a tank or healer make a big difference in your group’s success.
Tanking requires a bit more preparation than healing, because you're expected to know instances and lead the group. In low level dungeons though, you can get away with running ahead like a madman. The group will follow. If you screw up and pull too much and wipe, no one is likely to criticize you anyway, because they'll be thinking of their wait time for a replacement. You have to really, really suck to get kicked as a tank. I've done some profoundly stupid things while tanking, and have yet to be kicked from a group while tanking.
Players in LFD are incredibly tolerant of a large variety of tanking styles. Whether you meticulously mark everything and explain, or just run in and hit all your buttons, the group will go along with it. Silent tank, friendly tank or rude tank; chances are, they'll put up with you. If you are friendly, as I prefer to be, most groups will be friendly back at you and you'll have a great time. Some players will be rude and harsh your mellow, but that's what the ignore button is for. As a tank in a 5-man, you don't need to know what the group is saying, not even your healer. Just make the healer your focus and check that their mana is at a reasonable level. If they go AFK and you pull anyway and you wipe, they'll forgive you enough to finish the instance.
Here Be Dragons: PUGing Raids
The social advantage than tanks and healers had for 5-mans before LFD remains if you PUG raids rather than having a steady raid group. First, it's relatively easy to find a group. Second, as a tank or healer, your opinion tends to matter more. That means that you can affect the quality of the raid and the tone of the conversation in it more than if you were seen as a disposable DPS.
While PUGing raids is not for everyone, I've often enjoyed the role of bad-ass mercenary healer. You have to have a bit of a thick skin, and a relaxed attitude about the outcome of the raid, but it can be quite fun to heal under adverse conditions. When groups turn rude, I have a number of techniques to make the tone more positive, starting with the simplest of silly diversion, to discourses on the nature of fun and the challenge coordinating with players who don't know each other, and only occasionally do I have to threaten to take my toys and go home. Rare are the times when I had to leave the raid.
Yes, You Too Can Learn to Tank or Heal from the Comfort of Your Own Home
I haven't addressed the relative difficulty of tanking and healing as compared to DPS. New players shy away from these roles because they are perceived as difficult. They are slightly more difficult initially because solo play doesn't prepare you for them. But once you start grouping, which you have plenty of opportunity to do in these roles, you will have the benefit of practice and of advice from other players. Also, when I say casual, I mean players with limited time to play, not the incorrigibly lazy and the terminally incompetent. Any player with normal reaction times and half a brain can come to perform healing and tanking roles well enough to enjoy 5-man content.