If you turn off My Photo Stream in iPhoto, the following happens:
Photos are removed from the My Photo Stream album in iPhoto.
New photos taken with iOS devices using My Photo Stream continue to be uploaded to iCloud, but they aren’t pushed to iPhoto.
New photos you import into iPhoto no longer appear on the iOS devices in My Photo Stream.
If you turned on Photo Sharing in iCloud preferences, you can continue to interact with your shared photo streams.
Photos remain in iCloud for 30 days, and then they’re removed automatically. If you turn My Photo Stream back on in iPhoto, any photos that haven’t been removed reappear in the My Photo Stream in iPhoto.
Photos in My Photo Stream continue to appear on your iOS devices until removed from iCloud, unless you turn off My Photo Stream on a device.
Choose iPhoto > Preferences, and then click iCloud.
Deselect My Photo Stream, and then click Turn Off.
If you turn off My Photo Stream on a device but don’t turn it off in iPhoto, My Photo Stream continues to work with iPhoto and your other devices.