Project 3 - Is it okay to leave bits of a splitter unused?

When implementing C_2 (quad cost log delay) is it okay to leave bits of a splitter unused and use only 1 bit of the splitter?
for example:
proper_splitter_usage_question

It is not technically wrong, but such a design is not recommended. If you never need to use the zeroth bit of the output, why bother outputting it?