The extra sugar, like the one you add to coffee, or consume in chocolate and sweets.
Depends how much sugar you are already consuming, but in general fewer carbs in your diet can lead to more stable blood sugar levels and weight loss over time. If you are consuming large amounts of sugar, you’re more at risk for diabetes and heart disease, as well as other obesity-related healthy problems. If you aren’t eating a lot of sugar as is, and you don’t have health problems then reducing it likely won’t do much for you, other than some fat loss over time.