In the summer, ceiling fans are very effective at lowering the apparent temperature by making use of evaporation. When you are hot, you perspire, perhaps only a small amount. This is the body's way of cooling off - Evaporation of the perspiration pulls heat away from your body. Circulation of the air rapidly increases evaporation. The more evaporation, the cooler the apparent temperature. This means the thermostat on the A/C can be set higher - saving you money.
 

In a high hall or church
It may be best NOT to run the fans at all in summer. This lowers the demand for cooling since the hot layer on top is an excellent insulation between the cool air near the floor (and the people) and the hot roof and outside.

A large, tall manufacturing hall would typically have different goals. There one would have a floor full of heat producing machinery plus the people operating it, working hard and welcoming a bit of a breeze. Then it would make sense to run the fans at fairly high speed to create a certain and directed downdraft. And with the shifts going throughout the days of the week, the fans should be running all the time and maybe in all seasons.

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