When you upload photos to your Google + account, the auto backup creates a local copy of all backed up photos on your computer / laptop.
The folder is usually located under /Libraries/Pictures/Google+_Auto_Backup
Within this folder, there are a bunch of sub-folders organized by dates (as and when backed up). This local copy occupies a lot of space in your laptop / computer. In order to stop Google+ making these local copies on your laptop / computer, follow the process below:
Go to the Google+ Auto Backup icon in the system tray and click on it, then go to Settings.
In settings about the middle there is a Check box that you check if you want a local copy of the imported photos.
Uncheck it.
That's it. It'll stop creating the local copies of backed up photos on your machine.
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