Something that Austin and Jack talked about in the Introduction to Realis episode is that over the past few years they spent a whole lot of time talking about tokens and iterating how they work. As a GM, I absolutely love that players can discharge their token to use a Moon Sentence: it rewards them for playing into the theme of the setting and give us the opportunity to talk about them more. So with that in mind, I want moon sentences to be easy for them to use.
But I also know that moon sentences are an important way for the GM to throw wrenches in the PC's plans, and to give strong identities to enemy factions. A sentence like "Secret Police on [moon] always..." is extremely dramatic and descriptive of what a moon is like, but probably very hard for the PCs to use as their own means. The purpose of it is to give a specific view of who the bad guys are and what they do.
So: What are you thoughts on how easy/typical a moon sentence should be for the PCs to use? Is the answer just that it depends, and some stories want sentences to be easier or harder to justify using? Personally, I love when a sentence can clearly be used by or against the PCs: one of the sentences I'm most proud of writing is "Arguments on Areteas are always won by whoever speaks most," specifically because I can imagine it being used by everyone at the table over a game - or having a player intentionally never use it.