Why Can't You Just Use a Regular Spacebar?
Most modern social networks, games, and web forms automatically run a "trim" function on user input. If you submit a regular spacebar character (ASCII 32), the system detects it as empty and errors out saying "Field cannot be empty".
The Hangul Filler character (Unicode U+3164) looks completely invisible to the human eye, but computers recognize it as a legitimate typographic character, allowing you to have blank usernames or send blank messages!