When your Media Manager fills out with a lot of images, you will see the "lazy load" option show up in your manager. This option will save load time of your FTP, without this it could take several seconds or minutes for your whole Media Manager to load.
You will have 2 new options from this:
1. Load More - this will load about 10 more images to your list so you can keep browsing fast.
2. Load All - this will load ALL of your images, this could take a few seconds or minutes depending on how big your FTP is.
For more questions, feel free to submit a ticket to firstname.lastname@example.org.