Question

Why do you think it's important that we always label our units on word problems

Answer 1

Word problems describe a situation where something mathematical can be found out about a system. Often, it's a real-world measurement (like numbers of apples, ages of people, inches, feet, etc.) and usually have more than one object being discussed. 
The answer must be expressed in specific units so the value cannot be confused with other measurements discussed in the problem.