how does the purpose or focus of this career changes the photographers approach to taking a picture? Please explain how

It can change a lot of things like what you are trying to convey or even emotion.

Explanation:

When you take a picture you are telling a story about something. And what part of the contents you take a picture of can change your effect of a photo.

For example a speech

If you focus your picture on the speaker can change the effect if you are focusing on the crowd. You could take a photo of the crowd to rely the emotion of the speaker, etc. the list goes on.

You have to have a set goal of what you want to tell the viewer.