According to the FamilySearch Company Facts, as of January 2020, there are about 7.77 billion searchable names in the indexed Historical Record Collections with about 1.41 billion searchable digital images but there are another 1.73 billion digital images published only in the FamilySearch Catalog.
Now I need to explain a little about the Indexing Project. FamilySearch primarily used and current uses individuals volunteers to index the digitized records. You can read more in this article: "Indexing Makes a Difference." But as the FamilySearch Blog article entitled, "FamilySearch’s 2 Billion Digitized Records," states:
It’s important to note the difference between digital record images and indexed records. A large portion of the digital images on FamilySearch are unindexed. They can be viewed using an image viewer, but can’t be searched by name and other search variables like a fully indexed collection would be.
Anyone can help in the process of indexing record images like these after they are digitized. Learn more about how indexing works, and give it it a try.Now, finding the records on the FamilySearch.org website takes time and quite a bit of searching experience. I made this video a while ago to talk about this subject.
Where are the Digitized Records on FamilySearch.org
With all that, there was a need for a tool to find the unindexed records. The principal and really the only accurate way to find pertinent genealogical records is through identifying the exact place an event occurred in an ancestor's or relative's life. A general or vague place is almost entirely useless for research. Very few names are so unique that a name search will find only one particular individual.
Just recently, FamilySearch introduced the Historical Images Tool to help find those unindexed records. Hopefully, you already understand the need for this tool and will simply be thankful to have an easier way to search the Catalog but if you are just now learning where all the rest of the digital images are, I hope you understand what you have been missing.