First, it destroys your battery pretty quickly so once you plug it out, it will drain out in a matter of seconds.
Second, people care about hours due to the places that says "Requires ???? hours to enter" because when one admin is gonna open an hour-exclusive shop, theres gonna be the first people to enter it due to AFKing
Third, its sort of a reputation thing. Get more hours and you attract new players to believe that you have played the game for a really long time. However, most players are using hide hours so that means nothing anymore.
Last but not least, you miss out on events really easily..
Hide-N-Seek, Contests, and more will all be missed during the time you AFK for hours.
One more thing.. It logs you out if you AFK for too long so any messages you were supposed to receive are gone when you log in..