My Take
This is great resource for finding primary source historical documents. The language of old documents can be difficult for many students, but with teacher support and scaffolding the text can provide a greater amount of depth and perspective to historical events. There are a variety of other kinds of resources beyond the traditional government documents, including personal journals, photographs, etc.
How I Use It
I would use this for close and critical reading activities connected to social science. The documents and photographs available in the Archives can also be used for student-driven inquiry projects into historical topics.