The automatic copy option in the library within the Photos for Mac application is activated by default and this means that each photo that is added through the application to the computer in you will have your copy in the photo library (Photos library.photoslibrary) no matter where the original is. This means that the file that contains the library will increase its size exponentially, since it is intended for users who are not used to or are not interested in ordering photographs to save them in a specific location, this operation being carried out automatically by the system itself. .
However, we have the possibility to deactivate this option so that let us be the ones to manually organize the locations so that the Photos application is nothing more than a browser and editor of said photos without having any other function beyond that.
It is really not recommended to disable the option if we are not sure what we are doing or what this means, it is a feature aimed at more advanced users or simply that they are more aware of the manual administration of the photos. Apple has left this option as the default for good reason, since if it is disabled when we import photos from our digital camera or iPhone they will not be copied automatically or when importing one Aperture or iPhoto library to Photos.
If you have decided to do it with everything, carrying it out is very easy, we will only have to run the application and move to the Photos menu in the upper left to select preferences. Once we are inside, it will be enough to remove the verification check of the option "Copy items in the Photo library", from this moment there will be no backup for the photos that we manage within the application.
But if I have the photos in streaming, those are imported, right? Because when the iPhone is connected you don't have the possibility to copy the photos to another location.