it's bad.
the reason you eat many small meals throughout the day is to ensure a steady supply of calories and nutrients and to keep your
blood sugar and insulin at optimal levels. your body can only use "x" amount of calories, protein, carbs, vitamins, and minerals at a shot. if you eat more than that at a meal, the rest is converted to fat or excreted.
example, protein. let's assume your body can only absorb, say, 50grams of protein at a time but you need 175 grams of protein per day. if you sit down and eat 175 grams of protein, 125 of that will be converted to fat, burned as energy, or passed through the system. in other words, wasted. if, however, you eat 25 grams in the morning and then 50 grams at each of 3 meals throughout the day, you will be utilizing all of them.
of course, this is a grossly exaggerated example, but you get the idea.
same with calories - if you need 2000 per day but only need 400 at a shot and eat a meal with 700 calories, the
excess calories are not burned because they're not needed. they're stored as fat.
by eating only once a day, you also send a signal to your body: there's not enough food to go around. your body then starts emergency procedures, including turning down your metabolic rate by lowering your temperature, off-loading metabolically active tissue, and putting a priority on fat-storage for long-term survival. in other words, you lose muscle and more calories than ever are stored as fat.