Many apps that support the creation of wiki-links produce the closing brackets at the same time the user types the opening brackets. For example if I type [[ most apps will automatically add ]]
My copy of Agenda does not produce the closing brackets when I type the opening brackets and that creates a problem when I go and edit a piece of text, as the text that already exists is considered part of the wiki-link.
In addition when I select text in many apps and type the double opening bracket, or any character that has a corresponding opening and closing characters the app places both characters at either end of the selected text. This reduces friction.