Nomination and will are two different ways of passing the money after death of the investor. Normally Will deals with number of investments / assets and the details as to how the same will be divided among inheritors.
On the other hand, nomination deals with one financial asset (such as a bank fixed deposit, savings account, life insurance policy) and the nominee merely collects the funds on behalf of the legal heirs. Through will the amount of assets that will be inherited by each heir are clearly indicated, but nomination is merely a right to collect the amount and then re-distribute the same to legal heirs as per law.
However, sometimes a problem may arise, wherein an investor may nominate one person for his particular asset, but his / her Will may indicate some other person who has to inherite those assets. In that case, the Will will supercedes the nomination; and nominee will merely collect the funds and give to the legal heirs mentioned in the will.
In case there a nomination but no Will, then the nomination will be applicable. If there is no Will and no nomination, then the amount will be paid to the legal heirs on production of the Succession Certificate or any other legal evidence to show that they are the heirs. One has to apply in court for a Succession Certificate which usually takes a few weeks / months. To avoid such legal complications, the best way is to nominate and draw up a Will.
The other view is that the nomination process would override any title or interest of legal heirs.