"Sages, books, and rumors are all going to be of varying degrees of accuracy. Mostly degrees of inaccuracy, with some being flat-out wrong and others being mildly wrong or just misleading. Generally what they hear at least has some in-game value, in that they're hearing what some other people believe to be true. It's information that I as the GM am willing to cop to, to hand out, to hand to you to see what you do with it. It's information in play, out on the table, and not something that may or may not even exist."
- Internal vs. Extrernal Sources of In-Game Information
What is the role of sages in DF Felltower?
Sages are a way to let me, the GM, pass on information that might be difficult or impossible to reasonably get by adventuring to the PCs.
This could be the cultural background of part of the game world, or information about a general adventuring area ("Felltower" or "the Lost City of D'Abo"), or about a magical item you found.
Sages are also a way to develop a knowledge base of general, broad knowledge about the game world focused on a topic you're interested in. Want to know more about dragons? Hire a sage. Want to know more about orcs? Hire a sage. Want to know the history of the weird magic dingus you found? Hire a sage.
What isn't the role of sages in DF Felltower?
Sages aren't sources of rumors. They aren't sources of recent information. Generally, if you can find it out by going and doing in some kind of reasonably adventurous fashion, don't hire a sage to find it out. Go find it out.
Sages can't rattle off a list of "lost magic items of Felltower" for you so you know what you might find later.
They can't tell you recent news about a subject.
In short, "hire a sage" isn't a way to get out of scouting, traveling, and risk-taking. It's a way to get at information that you couldn't find out even if you did that.