When should I use the text_no_trim flag?

When a text overlay is applied on an image, it's first being separately rendered, trimmed and only then placed on the base image, therefore it may sometimes result in the following behavior (notice the changing heights of the semi-transparent bars):

Unless differently instructed, Cloudinary will trim the text container, and thus different bar sizes will show when using letters that go above or below the line. 

Adding the text_no_trim flag (fl_text_no_trim for URLs) to the text overlay transformation will override this behavior and will keep the margins around the text, for example:

Below is another use case example, where two independent text layers are needed two be aligned -