There’s basically never a reason to start the y-axis of your comparison graph anywhere besides zero.
It generated several dissenting replies, including one from me. Coincidentally, I had just reread part of John Tukey's classic book Exploratory Data Analysis (1977), in which he shows a good counter-example to that guideline. His example comes from a discussion introducing a variation of a box plot called a "schematic plot." He introduced the general box plot in 1969, and the schematic plot refined the box plot with a specific set of rules for the whisker lengths and outlier displays, which has always been the default in JMP where it's called an "outlier box plot."
Importantly, the measurements record the details about how the nitrogen itself was produced. The graph below shows the recorded weight (in grams per "globe") versus its source and the purifying agent.
The main difference is whether the nitrogen comes from air or not, which is how Tukey shows it. Here are some of his text and figures.
Although Tukey is comparing summary views (box plot vs. mean bar chart), his point holds for raw data as well. Here are JMP scatterplot versions of those plots.
It turns out that Lord Rayleigh's "nitrogen" from air also contained other elements unknown at the time, and the small differences led to the discovery of the element argon, for which he won a Nobel Prize.
So while a zero scale is often wise for comparison graphs, there is no substitute for making an intelligent choice. As Tukey suggests, the zero-origin plot doesn't make the case for a Nobel Prize.