If they're the same time scale you can easily compare what has changed over time. With different scales it's hard to match them up.

The graphs are independent and you can easily read each. What kind of comparisons do you want amongst them? Other than the 2 of them, the y axes of the graphs have different units.

On a phone they stack up vertically, in that setting it’s quite natural to want to have the time axis aligned too. It makes correlations stand out more.