I am fully on board. People use a lot of stuff on their phones where screen space is precious so judicious use of an emoji here and there can really help both in terms of compressing more content on the same screen and making it a bit more expressive.
That being said, replacing the literal “cat grinning” text with an emoji that’s technically called “grinning cat” is confusing and I wouldn’t find it helpful. It changes the text from “Why is your cat grinning?” to “Why is your grinning cat?” which kind of sounds like Drax in “Infinity War” famously exclaiming: “WHY is Gamora?”. 
