UPDATE 2020-01-02: Since the release of InDesign 2020, more image fitting options have been added, such as “Keep Existing” in the Data Merge content placement options panel; and Content Aware Fit that was introduced in InDesign CC 2019. However, this article will remain for posterity.
Adobe InDesign’s frame fitting options can be quite useful, but with ten possible combinations it can be difficult to remember what fitting option to use.
Rather than use trial and error, why not refer to a chart which I’ve made especially for this purpose?
The downloadable PDF version for print is available from this link.