The Trim feature is sort of like a “Smart Cropping” tool. It automatically removes excess, unused area from around the image.
There are a few popular cases where the Trim tool can be handy in saving you from having to manually drag each edge of your canvas toward the edge of the image.
As a rule of thumb, trim is great whenever you have labels, numbers, or callouts hanging “off” your central image. I made a quick, informal video showing a common workflow where Trim comes in handy. This example is from the Mac, where Trim is located under the Edit menu. On Windows, you find Trim under the Image tab.