I use it for sites like Facebook where I want to type :) without it changing to the terrible `U+1F642 SLIGHTLY SMILING FACE` [1]. I wouldn't really mind if it were the `U+1F60A SMILING FACE WITH SMILING EYES` [2], but the first one is so laughably terrible, as if I'd really want to send an emoji to communicate a disingenuous, pained smile as a default. Some platforms let you backslash-escape sequences so they don't get turned to emoji, like \:), but for Facebook and the like, putting a ZWS in between the letters stops the conversion.

Though if your emoji is at the end of a line, it'll potentially break your emoji between the two lines. since That's what a ZWS is for, after all.

1. https://util.unicode.org/UnicodeJsps/character.jsp?a=%F0%9F%...

2. https://util.unicode.org/UnicodeJsps/character.jsp?a=1F60A&B...