For the same reasons you'd want to use italics in a proportional font - for emphasis or contrast.
1. Syntax highlighting which uses both color and font style, e.g. class name are italicised by default in my editor (Sublime Text).
2. Editing markdown/HTML files with italics tags/markup.
3. Also, italics also work on the console, and some console/TUI apps may use it.
For the same reasons you'd want to use italics in a proportional font - for emphasis or contrast.
1. Syntax highlighting which uses both color and font style, e.g. class name are italicised by default in my editor (Sublime Text).
2. Editing markdown/HTML files with italics tags/markup.
3. Also, italics also work on the console, and some console/TUI apps may use it.