Apple's new Photos app is a great way to import, manage, edit and share your digital photos. As you add more photos to your library, however, that Photos Library file has the potential to grow out of control pretty quickly, gobbling up every byte of free space that you have.
To avoid your Photos Library occupying too much of your drive's available space (resulting in a sluggish system), it's a good idea to periodically archive older photos. Because we're all different, there is no one-size-fits-all archival strategy, but there are some tips that will make archiving your older photos easier. To help illustrate, here is the process that I go through.
First, it's important to note that I usually keep about 2 years worth of photos in my Photos Library. Before deleting my older photos, I go through a process to archive them to another location (Dropbox) first. Dropbox is great because I consider it to be near-line storage. Essentially, that means that it's not as easily accessible as if the photos were still in Photos, but it's also not too much of a pain to access them when I need them. Within my Dropbox account, I have a folder called "Archived Photos". Inside that folder, I have folders for each year... "2005", "2006", "2007", etc.
When January 2016 rolls around, I will create a new folder inside my "Archived Photos" folder on Dropbox called "2013". This will contain all photos taken during that year.
Next, I will search for all photos that were taken between January 1, 2013 and December 31, 2013. The easiest way to do this is to create a new "Smart Album" (A Smart Album is an album where its contents meet a specific set of criteria). To do this, we will go to New > New Smart Album...
When prompted, we will enter our search criteria...
In this example, we will choose to filter on "Date" when the date is within a specific range. Before clicking "OK", we can see that this search will yield 3,940 photos.
Once we have clicked "OK", a new Smart Album has been created with the name "2013". These Smart Albums are easily identifiable by their gear-looking icon.
Next, we will simply select all images within that Smart Album. The quickest way to do this is to select an image then press Command+A (All). All images will be selected. Next, we will export these photos to a folder for archiving. There is the RIGHT way to do this, and the WRONG way. The WRONG way is to simply drag and drop the photos from Photos to a target folder. This is the easy way, but doing this will also compress the photos and convert RAW-formatted files to JPEG. The better way to properly export these files is by going to File > Export > Export Unmodified Original...
Next, we will choose the location for these files to be exported to. Because I have already created a folder called "2013" in preparation to store these files, I simply navigate to that folder and choose to export.
After the files have finished exporting, you will want to confirm that the number of files inside that new "2013" folder matches the number of photos in your 2013 Smart Album. If it does, you are safe to delete the photos from the Photos app!
If this is the first time you have attempted archiving photos from Photos, you will want to go go back and apply this same principal retroactively to all older photos in your Photos Library. For example, you may want to archive all photos taken in 2000, then 2001, then 2002, and so forth until you are caught up. Yes, it will take a little time to do this, but it will save you a LOT of time and storage in the long-run.
One more note about archiving to Dropbox (or any other cloud-based storage solution). When the files are initial exported to this location, they are not only available from the cloud, but a copy (the initial copy) is still stored on your computer. Once the files have had time to finish syncing to the service, you will want to go into your settings and disable syncing of that folder. This will remove the photos from your computer, but they will remain in tact in your Dropbox account (which you can access via dropbox.com or the free Dropbox app on your smartphone or tablet). Doing this will allow you to reclaim the space that those photos were taking up, which was part of the original intent of archiving the photos in the first place.