I have clients who are a classic blended family. She had a child young and separated from the father when her daughter was three; he divorced his wife when his daughter was seven; when they married, they had a child together. They consider all three children to be both of theirs, as they have jointly raised them all, but he never adopted her daughter and she never adopted his. They have drafted their wills to reflect their view of their family rather than their legal status.
Pop quiz: what would have happened if they hadn’t done wills?
Given that most of their assets are jointly held, on the death of the first to die, the survivor would receive everything. However, on the death of the second partner, only that person’s children would inherit. If she died first, her daughter would receive nothing, and vice versa. This would have been completely contrary to their wishes.
Even if you have a cookie-cutter family, you should consider having a will. If you fall anywhere outside the norm, it is vital.