If every Terminator was designed for a specific purpose, what was the T-1000 designed for (role in the future)?

From the many kinds of Terminators in the franchise, we learned that the T-800 were used for infiltration.

What exactly were the T-1000s used for?

From the Universal Studios promotion, it was shown that these HUGE spider liquid terminators were mainly for protecting the base, so one could say the last line of defense?