It means more images are available on familysearch.org at the library than are available to you at home. Because of the varying contractual relationships between FamilySearch and the owners of the original records, FamilySearch has a lot of images that they’re not allowed to display to the public on their website. Those image collections are marked in the FamilySearch Catalog with this symbol:
and if you try to view them at home you’ll get a pop-up saying that you must visit either a Family History Center (like the FamilySearch Library Oakland) or a FamilySearch Affiliate Library (like the CGS Library) to view the images. Note that there are some collections with even more restrictive contracts and in those cases the dialog box will say that only a Family History Center will do.
To make it a bit more concrete, suppose you’re working on a family in Hardwicke, Cambridgeshire, England. FamilySearch has the Bishop’s Transcripts for 1599-1875 (https://www.familysearch.org/search/catalog/828833) available with no restrictions, but they also have the original parish registers (https://www.familysearch.org/search/catalog/207037) from which those transcripts were transcribed. Of course you want to look at the original registers! They’re restricted, so you can’t look at them at home and until a week ago you couldn’t look at them at the CGS Library, either. Now that the Library is a FamilySearch Affiliate you can look at those parish register images at our Library, you don’t have to go up the hill to the FamilySearch Library.
Register now for your library session to use this new resource!