from "Mr. Tuppence":
The Dead Sea Scrolls come from two different time periods: those prior to 79 A.D. which were in one set of caves, and those from around 100 A.D. from an entirely different set of caves.
The communities which copied the Scriptures prior to 70 A.D. have done so from a different text type to that used after 100 A.D. The earlier text type is the Hebrew equivalent of what is quoted from the Old Testament in our New Testaments (in Greek). In contrast, our Old Testaments today are basically translated from documents based on the later text type. This is why the quotes we read in the New Testament are often not quite what what we find in our Old Testaments (the verses quoted). It is usually assumed that it was the Essenes who were responsible for the copies found from the early text type material. The later material dates directly from the Council of Jamnia, held about 100 A.D. where a different text type was introduced, as well as different Hebrew characters. (In this later text type, the vowel points were not inserted until 900 A.D. They were inserted on the basis of oral tradition)
They are interesting historical documents. The earlier texts confirms the accuracy of the Greek version of Scripture known as the Alexandrian Septuagint.