I need to add songs into iTunes Library but I don't want to copy songs into library. While drag and drop just copies all songs which needs to be added to the Library folder and then uses it. So, we have waste of space twice, from where we copy songs and to where we copy them. But I don't want to copy songs into Library folder, I just want to add it into Library and play or sync with iPhone. So, at only one place all songs can be managed.
Uncheck Keep iTunes Media folder organised and Copy Files to iTunes Media folder when adding to Library
Screen shot provided by @Wheat Williams:
Option (alt) dragging them in the library will not copy them.