The description of this property is quite vague, and poorly worded. Additionally, setting this property to an empty string does not override the TextChatMessage’s Text to an empty string, but instead defaults to not overriding at all. I believe this behavior should be mentioned in the property description, as it is quite unintuitive.
Page URL: https://create.roblox.com/docs/reference/engine/classes/TextChatMessageProperties#Text