For many people, a large part of the purpose of a will is to make sure that their estate is distributed the way that they want it to be distributed. Unfortunately, fights between surviving relatives over who was given more than their fair share or who was denied what they feel is their due can drag an estate into court. If successful, a challenge can prevent your original intentions from being carried out. Even if a challenge isn't successful, it can take years to resolve and prevent your rightful heirs from moving forward.
Do you suspect that your relatives are likely to start fighting over the contents of your will the moment after you're gone? One way to limit the potential for legal challenges to your will is to add a no-contest, or "forfeiture," clause. This is a clause that says that an heir who challenges the will and loses gets nothing at all. If done right, this can make someone hesitate to gamble a sure thing against an uncertain legal decision in the future.