Everyone should have a will.
People often assume that when they die their estate will go to the people they want it to. Unfortunately, this does not necessarily happen if there is no will and you die intestate. Under intestacy rules there is a specific order of inheritance which may not reflect what you assumed.
This is particularly relevant where a couple cohabit and are not married or in a civil partnership. For example, if a couple with no children cohabit and the house is in the sole name of one of them, without a will bequeathing that house to the cohabiting partner that partner will not inherit.
It is also relevant where there is a second marriage and providing for children of the first marriage is important.