Having balls in a game can be a double edged sword. I would imagine one could be prone to back ache staring at them all day but on the other hand they could tell you many things about yourself you may not know, whether you like it or not. This may be a case of professional ethics for a hard working Seer, or perhaps knowing too much about ones own future would be enough to drive one insane. I could see how there may be an addiction issues for some content but one could permissibly have a polish over an occasional glimpse.
But dropping balls into a fantasy game is an excellent way of funnelling clues to players and whilst one can scry into the future, there is no reason that a device couldn't be a useful communication tool, particularly for realms that lack industrial transport or technologically advanced teleportation, a sort of bronze age broadband. By the same token, one can see into the past if there are important messages hidden in the history of a world, or perhaps portents from those long and mostly departed.
Clues, cues and influence have to be just right though. Too little or enigmatic information is just frustrating and equally having a demi-god at the end of the line can also be somewhat overwhelming both with regard to reverse charges as well as not being able to hang up. For my part I prefer to add a physical reference to any scrying session, items and locations, which provide a definite anchor to any speculation and a well defined jigsaw piece for a larger puzzle. And just to make sure party members don't walk around with a plot device all the time it's important to make balls nice and large.