So you need to implant steers with a growth hormone to compensate for weight loss. Bulls are cheaper than steers but, there can be handling problems and bulls will sell at a discount to steers at market time. But, light weight calves can also spend more time in the sick pen and have a higher death loss than do heavier calves. This a function of age, stress and the ability to adapt to conditions. The same can be said for frame size and grade.
Size helps indicate the animals potential carcass size and feeding efficiency.
Medium framed calves are the norm. Large and small frame calves are frequently cheaper to buy but, they are also discount when you sell them. Size can also denote breed type, the environment the calf grew up in and its ability to gain weight efficiently. USDA feeder calf grades denote carcass quality and can suggest the yield potential of the calf. A No.1 designation suggests an animal with more muscling than a No.2 and a No.2 grade has more muscling than a No.3.