I’m expanding on an existing forum entry here: Bring window to foreground instead of opening new one?
The ‘subl’ command always opens folders and projects in a new window, instead of bringing any existing window to the foreground.
Additionally, running ‘subl my_file.txt’ will open the file as a tab within an existing window, regardless of whether that file is contained within the folder/project specified by that window. I think it should instead only do this if the file is contained within the window’s specified project/folder, and open a new window otherwise.