The 18th Century corset is one of the most comfortable to wear, it supports the bust and back without squeezing the waist. They can be worn to create the proper silhouette and support for the historical costumer, or as a modern fashion style, if you're into that sort of thing.
During the French Revolution and the Napoleonic Wars, the neo-classic styles came about. There was the revival of the Grecian "zona" and cotton materials for dresses. Cotton had become popular near the end of the 17th century when it had been brought from the east. The dresses became softer and looser. The natural contour of the body was now fashionable, and so stays in corsets were now discarded, causing much more comfort than before.
For those not having the beautiful curves the fashions demanded, they resorted to confinement of their figures to fashionable bounds. This soft cotton also introduced the first two piece dresses to be seen in two centuries. This fashion at the end of the century and beginning of the 19th century was called vetue a la Sauvage.
Now, be nice to your costume designer. Because those corsets can be tight...