In a campaign I'm in now, everyone is after it. Noone is sure what it does. One group wants it because it can tell the future. Another one wants it because they believe it to be an all powerful speelbook. There are like 10 different groups after it, for ten different reasons. My character wants it to find a family artifact, and as a bargaining chip with the other groups. I think they left it vague for just this reason. To let DM's drive players crazy with the unknown.

We'll probably find it and it will turn out to be a simple calender figured out to 2,000 years. Not magical at all. lol.