Making weekly menus can help you stick to your eating goals -and- save you money. If you plan your menus around certain ingredients, you can cut down on what you need to buy. Example - I'll make chicken enchiladas and use the shredded chicken in soup or sandwhiches later that week.
It also helps you to use your weekly sales and coupons better, you can plan meals around what's on sale, and what's in season for a better price. And having a list -always- helps you save money if you stick to it (and helps avoid temptation to buy things that aren't healthy for you).