If you die before executing a will, then Massachusetts probate law will automatically determine what happens to your estate. The law decides who will get your property and how much each person will receive without any input from you or the people you care about. Your surviving family may not receive what they expect or what you would have wanted them to receive, and they will not be able to challenge the distribution.
Not all of your assets will go to your spouse. Half will go to your surviving spouse and half to your children. If there are assets with both your name and your spouse's name on them this can get pretty complicated. For example, if you have a family business that you co-own with your spouse, half of your ownership will go to your spouse and half to your children. A legal guardian will have to be appointed to manage your children's interest in the business until they are 18. Your spouse can be that guardian, but will have to deal wtih the cost and hassle of going to court to get appointed as guardian. Also your spouse may have to post a bond to the probate court and provide detailed accounting to the court for all business transactions.
If you are survived only by a spouse, most of your estate will go to your spouse but part of it will go to your parents. Again, this may not be what you would have chosen.
If you are survived by your children only, then your whole estate will pass to them. If they are under 18, a guardian will have to be appointed to manage assets for them. This may create an unintended burden on surviving family members who will have to navigate the probate system to appoint a guardian.
Think of all the headaches, frustration and legal expenses you can spare your family by putting a will in place. Then, if you predecease them, they will at least have the comfort of your affairs having been left in order.