A long time ago, in my first MMORPG experience, I concentrated all my efforts on my main ... a smite cleric. So, DAOC taught me to diversify!
My first main in WoW was a dorf hunter, because the first cinematic made them cool. My second main was also a hunter, followed by a shaman ... then ... well, the only classes I have never managed to get to max level in any expansion are rogue and warrior, and I may yet get a warrior there.
I enjoy playing so many, because as another poster already stated, I like getting to see what the various classes can do. The downside, at least for me, is that I play a bunch of classes fairly well, but none expertly.
Getting alts and their crafting to max level is easy. Outfitting them with gear decent enough to PvP without insta-death - that does get a little tiring.
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It smells like the left wing of the day of judgment.
- Herman Melville