why do you need a will
If you want to leave any part of your assets to charity, you obviously need a will. If you want to benefit both family members and charity, there may be ways in which you can reduce the taxes for your family through special charitable trust arrangements.
A will is even more essential if you want to leave assets to a partner you're not married to. Most states' intestacy laws are brutal on unmarried couples. Your live-in partner of 20 years could get nothing and be forced from your shared home.