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There are some who will abuse it to vote up each of their accounts, but some may want to serve different audiences. I know some who do all their Actifit posts from a different account so they don't fill up their main feed. We are allowed to have as many as we want, but I think Steemit aim to only supply one per person as they have to delegate to those.

Oh yeah, I understand :) As of now one account feels already a bit grindy for me, so maybe later I'll have some others too. Also often the drugwars fight reports, "see what I opened today on Steemmonsters", etc. posts are not seen as high-quality posts, so it is indeed a good idea not to have them on your main account.
I just realized that on multiple accs you could farm the steemmonsters dailies multiple times. If you gather the cards to one of your profiles you can have so powerful decks...

I'm sure people do run multiple Steem Monsters decks, but you would have to buy cards for each of them. I don't have time for that.

What I'd like is to be able to filter what tags I follow for certain people to keep the feed under control. Maybe one of the dapps will add this.