Prenuptial agreements protect assets. However, sometimes they are planned to prevent certain behaviors.
Prenuptial agreements are set up to equalize assets such as when one or both parties enter the marriage with children from a previous relationship. It is an agreement that is arranged so the couple come to terns with potential issues beforehand.
However, some people try to do more with prenuptial agreements, according to Market Watch in "Prenuptial agreements contain more bizarre 'lifestyle' clauses."
Prenuptial agreements are now being used to guard against undesired behavior by future spouses.
For example, some agreements now penalize a spouse for cursing, gaining too much weight or hanging out with friends too much.
The problem with these agreements, besides the obvious who would want to marry someone with those types of demands, is their enforceability.
Courts have a tendency to look at agreements as being serious, as well as being fair and beneficial to the parties involved.
Reference: Market Watch (Sep. 9, 2017) "Prenuptial agreements contain more bizarre 'lifestyle' clauses."