Perhaps silly iCloud photo library question

[jabingla2810]

I have enabled iCloud photo library on my Mac, and uploaded all my photos and videos.

If I now enable it on my iPad and iPhone, what happens?

Do the pictures stored locally on those devices also get uploaded? Making duplicates of all the photos that are already in the iCloud library?

Should, I delete all photos from these devices before enabling iCloud Photos?

 

[sualpine]

I have enabled iCloud photo library on my Mac, and uploaded all my photos and videos.

If I now enable it on my iPad and iPhone, what happens?

Do the pictures stored locally on those devices also get uploaded? Making duplicates of all the photos that are already in the iCloud library?

Should, I delete all photos from these devices before enabling iCloud Photos?

There is no duplicate detection that I have found. That's why I can't use it.

 

[jabingla2810]

There is no duplicate detection that I have found. That's why I can't use it.

So I should probably delete all photos on my iDevices before I enable it?