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It doesn't really make any sense. I realize that F2P games use the grind as 'stick' in order to get players to buy stuff from the cash shop, but aren't there more immediate ways that you can "encourage" your player base to buy that crap. If the goal is to get people to pay for junk, time seems like a horrible way to do it since there will always be people that are willing to waste their lives rather than pay for anything.
The same question applies to subscription games. When your players spend huge amounts of time playing your game, the bandwidth costs eat up your revenue. The less time people play per session, the more money you make because you aren't spending as much on bandwidth. Rather than demanding players sit on their asses for 20+ hours a week, why not just use that sub money for monthly content expansions. You could still do one major box expansion every year just to get a spike in returning players.
I just don't see endless grinding and tedious OCD gameplay as a win-win situation for developers, publishers or gamers. There are more effective ways to keep people paying those subs and buying those items.