Discretionary ligatures are typically decorative in nature and should be used very sparingly, lest legibility deteriorates. See the examples at [1].

[1] https://www.fonts.com/content/learning/fontology/level-3/sig...

ah, like this example here: https://justmaku.org/2018-06-19-amazon-leaking-ebooks

the st ligature is startling every time i see it, tripping me out of the flow of reading.