A lot of game designers shoehorn grinding into the game to make it seem longer. Y'know, it has 12 hours of gameplay as opposed to 6 because you have to grind before every boss. Not really a design flaw in that sense but a really shitty design strategy.
In some RPGs it works, though. If there is a large emphasis on collecting various things (take Persona, for instance), it allows one to broaden their selection of tools of destruction in order to just completely murder a boss or something. I never got into Etrian Odyssey for a similar reason, though... I shouldn't have to level up to 7 on the first map to avoid getting slaughtered by one unlucky random encounter.