When you plug an iOS device into your Mac, you no doubt end up launching iPhoto, whether you intended to or not. Yosemite handles the setting that controls this in a way different than its predecessors.
By default, when you sync an iPhone or iPad, OS X opens iPhoto, asking you if you want to import photos. I had this setting turned off in Mavericks, but it seems to have been turned on again in Yosemite. Yet when you look in iPhoto, there is no such setting. Tricky of Apple to have hidden it in another app…
Read the post for the details. Good stuff.