For starters, most venues will require you to show proof of event insurance to use their space. Beyond that basic requirement, large groups, alcohol, and rented spaces put your assets on the line; event insurance can protect you.
If you chose the menu and a guest has a serious allergy to fish, you could be on the hook (pun intended) if they end up in the hospital. If someone busts a move which in turn busts a window, you can expect the venue to pursue some money from you for the repair.
Say a guest is “overserved” and winds up injuring themselves or others once they’ve left the party. You could be hit with a mountain of problems way worse than any hangover.
Events mean risk, and risk means you need insurance.