I absolutely started weighing when I realized that I really had to watch my calories to lose weight. I lose at 1100ish calories, but stall at 1300-1400- so you can see how being off my a ounce or so in a meat portion (and things like steak or salmon can really pack a calorie punch) could really screw me up. I've found that depending on the shape of the peice of meat my estimation can be totally off - I overestimate the size of peices that are "cube-ish" and underestimate the size of flat things (hello no visual-spatial skills!! ).