Quick Chat allows you to easily select a member to chat to.
When to want start chatting to a member:
You press the Alias of a member, their profile shows on screen.
Then you have to also press Chat To - top left in the profile - to select to chat to that member.
However if you have turned Quick Chat ON, using the hamburger at the right of search:
The member is auto-selected to chat to when you press their Alias.
You will also see their profile.
see also: Chat to a player