iPhoto can comfortably manage as many as 25,000 photos in a single collection, give or take a few thousand, depending on your Mac model and how much memory it has.
But for some people, 25,000 pictures isn’t a very distant threshold. As your collection of digital photos grows into the tens of thousands (and if you have a digital camera, this will happen sooner than you think), iPhoto eventually starts slowing down as it sifts through more and more data to find and display your pictures. At that point, scrolling the photos in the main Photo Library becomes an exercise in patience that would drive a Zen master crazy.
When your Photo Library becomes too large to manage comfortably, you can always do what people used to do way back in iPhoto 2, when the limit was only 2,000 pictures: Archive some of the photos to CD or DVD using the Burn command described earlier, and then delete the archived photos from your library to shrink it down in size. For example, you might choose to archive older photos, or albums you rarely use.
Remember, archiving photos to CD using the Burn command doesn’t automatically remove them from iPhoto; you have to do that part yourself. If you don’t, your Photo Library won’t get any smaller. Just make sure that the CD you’ve burned works properly before deleting your original photos from iPhoto.
The one disadvantage of that offload-to-disc technique is that it takes a big hunk of your photo collection offline, so that you ...