You can decide who should benefit following your demise. You are said to have died intestate if you die with out Making a Will. Intestacy rules then apply and the loved ones that you believed would receive your assets may receive little or nothing.
You can appoint a person or people that you personally now and trust to look after your assets until the children become old enough to take responsibility themselves.
Similarly, you can appoint guardians who will be responsible for your children's upbringing if neither parent is alive if you have young children. The Courts might choose someone for you if you do not leave a Will, and that might not be someone you would have chosen yourself.
There may be some opportunities to do some financial planning for yourself, to reduce Inheritance tax, or how you leave things for others. IHT is much less of a problem for many people but there are still plenty of people around who could benefit a great deal by organising their Will properly.
I’ve come across too many instances of people dying without Making a Will both professionally and personally. To speak bluntly, it’s a lot of additional hassle and upset and even financial difficulty to bereaved relatives when some passes away without making a Will.