- Some hands where they think slam is making.
- A similar number of hands where they think it isn't.
- All the hands where they don't know whether slam is making or not.
If you follow this strategy and then the opponents bid slam, with the first category of hand you should save; with the second you shouldn't; with the third you should
Edit: That's an oversimpliciation, of course: in real life the hands won't fall neatly into these categories. Instead, the 5♥ bidder's expectations will be in a continuous range from "Probably making slam" to "Probably not making slam", but the aim should still be to have some sort of symmetry around the "No idea" point.