Not the primary use case for stickers, but what do you do when you're talking with someone for whom you're not literate in their language? Or someone who is not literate in any language?
Stickers provide utility beyond beyond a fun way to communicate. Stickers, emoji reactions, voice notes, etc. are things we tend to see denigrated here, but are also non-optional features for a messaging app in the year 2016.
These days messaging apps have been translation features. Another thing that matrix/element is missing sadly.
I remember reading a feature request and it was put off on the reasoning of "server-based breaks our encryption and client-based doesn't work well enough". Makes sense but I don't think the latter point is still true, and Matrix is too focused on encryption IMO. In large open rooms there's no point to it because anyyone who wants to can join anyway.
Stickers provide utility beyond beyond a fun way to communicate. Stickers, emoji reactions, voice notes, etc. are things we tend to see denigrated here, but are also non-optional features for a messaging app in the year 2016.