When the duty cycle is very large, for example, 90%, the gain is large, 10 in this example, the input current is 10 times larger than the output current, which increases the power losses in the input inductor due their conduction losses, usually modeled as an equivalent series resistance esr, furthermore, the current in the mosfet is large and remains almost all the time, it is possible to design it, but in the practical design results cheaper using other configurations such as the flyback for example.