I think these choices are more context specific than is often appreciated. For example
> if I have measurements [A: 100, B: 101, C: 105], and then scale the axes to "fit around" the data (maybe from 100 to 106 on thy y axis), it will seem like C is 5x larger than B. In reality, it's only 1.05x larger.
If you were interested in the absolute difference between the values then starting your axis at 0 is going to make it hard to read.
It is however very rare that absolute differences matter; and even when they do, the scale should (often) be fixed. For example the temperatures:
[A: 27.0, B: 29.0, C: 28.0]
versus:
[A: 27.0, B: 27.2, C: 26.9]
If scale is fit to the min and max values, the charts will look the same.
Still, as a rule of thumb, when Y axis doesn't start at 0, the chart is probably misleading. It is very rare that the absolute size of the measured quantity doesn't matter.
Yeah, you should graph both starting at 0K right? You wouldn't want to mislead people into thinking somthing at 10C is ten times more hot than something at 1C.
> if I have measurements [A: 100, B: 101, C: 105], and then scale the axes to "fit around" the data (maybe from 100 to 106 on thy y axis), it will seem like C is 5x larger than B. In reality, it's only 1.05x larger.
If you were interested in the absolute difference between the values then starting your axis at 0 is going to make it hard to read.