When you upload photos, the photos get resized and optionally watermarked. Here you can set the quality of that resize.
The higher the number the higher the quality ... but also the higher the file size which will take longer to load.
See this article for more information on resize quality.
Thumbnails Per Page
The thumbnails automatically populate as you scroll down the page, but after a while it can slow things download if there are a lot of photos in a gallery. Here you can limit how many total populate. Once it hits this limit, then they are presented with next / previous and page options.
Suggested setting is 200.
Download Zip File Limit
This will set the number of photos to put in a zip file when someone purchased multiple downloads on an order. When there are more photos than the limit, it will create multiple zip files to download. This is done because too many photos in one zip file can cause server errors.
View All Photos Default
This set the default sort view when viewing photos in the All Photos section.
FTP Upload Process Settings