There may be family members or people close to you that you do not want to inherit under the terms of your will. Alternatively: you may want them to receive less than they might expect. This can be for all sorts of reasons such as estrangement, or because you gave someone large gifts during their lifetime.
This situation can lead to confusion or dispute. If a beneficiary feels jilted or if they do not understand what has happened they may mount a legal challenge to your will.
If you do not want someone to inherit under the terms of your will you should not mention them at all. Do not leave a 0% residuary to them. This can lead to further confusion.
If you want someone to inherit a smaller sum you can set this gift out in the residuaries or the Specific Gifts section of your will.
To reduce the chance of confusion you can leave a letter of wishes with your will. This can set out further detail and narrative as to what has happened. Remember your will becomes a public document once you have passed away. You may not want the world to be able to see.
If you believe that someone is likely to challenge your will please ensure you do what you can to protect your wishes.