While collecting and preparing data, a difference between questioning and observation is that questioning approaches

I believe the answer is: enable researchers to collect a wider array of data

Observing is being done by paying attention to the subjects. The amount of data that can be obtained is limited to the things that shown by the subject. Questioning is being done by asking the subject directly. So, we can ask the subject on why they do what they did and obtain a more deep and profound data compared to observing.