The usual reason for entering into a deed varying a will within 2 years of death, is to secure an inheritance tax reduction or to skip a generation so that a gift is removed from an affluent beneficiary and diverted to his impecunious children.
We have recently been involved in another scenario where a deed of variation came to the rescue. A will had left children of the deceased rather dissatisfied because the principle of equality had been ignored. The siblings were able to reach a satisfactory arrangement amongst themselves and the will was varied accordingly. It was also able to set out the basis on which jointly owned property would be held.