It is not helpful in general. Magnitude and relative changes are different things. Sometimes you need one, and sometimes you need the other.
Global average temperatures are a good example: where is the zero? Is it significant? The effects of an increase or decrease of 0.5°C are massive, so the appropriate way of presenting this is to show the temperature anomaly, not the absolute temperature. Also, this way the information is conveyed regardless of the temperature scale in use.
The religiosity graph is interesting. If you want to show a sudden change at some point, then showing the relative change is appropriate. If you want to show that people are not religious anymore using this graph, then you are dishonest. It is all about the narrative and the point you want to make.
On its face, “scales must go to zero” is not good advice, because you can always change the variable so you can make anything go to zero without changing the shape of the curve and our perception. However, when we see a graph, then we always need to understand why it goes to zero or not, what the author is trying to show, and whether they are being honest about it
"global average temperatures are a good example: where is the zero?"
I don't know.
"The average surface temperature on Earth is approximately 59 degrees Fahrenheit (15 degrees Celsius), according to NASA"
But I know if the average temperature increased 0.5 degree C and I show a graph with the scale 14 to 16 degrees over time and the headline "world average surface temperature exploding" then this is excellent clickbait and a nice graph, but it is misleading on the first look.
It is not helpful in general. Magnitude and relative changes are different things. Sometimes you need one, and sometimes you need the other.
Global average temperatures are a good example: where is the zero? Is it significant? The effects of an increase or decrease of 0.5°C are massive, so the appropriate way of presenting this is to show the temperature anomaly, not the absolute temperature. Also, this way the information is conveyed regardless of the temperature scale in use.
The religiosity graph is interesting. If you want to show a sudden change at some point, then showing the relative change is appropriate. If you want to show that people are not religious anymore using this graph, then you are dishonest. It is all about the narrative and the point you want to make.
On its face, “scales must go to zero” is not good advice, because you can always change the variable so you can make anything go to zero without changing the shape of the curve and our perception. However, when we see a graph, then we always need to understand why it goes to zero or not, what the author is trying to show, and whether they are being honest about it