RF transformers in first, second and third IF stages, how and why are they different?

Many websites about RF transformers talk about IF transformers to be implemented in first (green slug), second and third (brown, black or orange slug) 10.7 MHz IF stages. Other than this, I don’t see any elaboration on why transformers with different impedance ratios would be used for the cascaded stages.
So what is the difference and why is it important?