Yosemite's behavior is a step backwards from Mountain Lion's. (Don't know about Mavericks.)
In ML, you were *prompted* after the import as to whether you wanted to delete the photos. That makes sense logically-- import first, *then* figure out if you want to delete. IIRC, you could even choose to delete selectively!
Now, the sequence is reversed--and you aren't even *asked* whether you to delete. You have to pick deletion *before* import. But, worse, you have to *remember* to check the "Delete after import" box *every* time you import. If you don't, you end up with photos still on your iPhone or iPad. Next time you come to import, it willy-nilly imports them *all* *again*. That's unlike in Mountain Lion, where you would be notified of duplicates and that you had already imported the photos. It would even prompt you if you wanted to import just the fresh ones. So, in Yosemite, you can end up being stuck with gobs of duplicated photos.
I could even live with that (not really! 🙂 ) save that Photos does NOT show the image name or info below it to make locating and removing duplicates easier.
I'd be happy to learn of some preference settings in Photos that I've overlooked that could solve all this!
Now, about those barely visible dots that replaced fully-colored items in List View... 🙂