My mother passed away suddenly. I was her only child & she had a partner, but they were not married. She did not have a will (even though she bugged my father constantly about having one). It made grieving & the whole finical experience miserable. I had to figure out what accounts she had, find out how to transfer them, transfer them to my name & it felt like a never ending reminder that she was dead. And it didn't stop after a few months. This took YEARS. I don't think she wanted to put me through that, and I learned a lot, but if you want your kids to be able to move on with their lives, leave a will.
I also went through the nightmare of having to deal with her partner who was a controlling doctor. He made the situation a million times worse by adding his name as her spouse to the death certificate (it takes 9 months to get a new one) which I had to change. The problem is less the laws that protect the fact that her assets were rightfully mine, but other people, the grieving & the overall confusion involved if you have many different finical accounts.