Ideally, UAT testing should provide the opportunity to uncover any remaining bugs, and to test usability directly in the operational environment. These tests should generate a confident certainty that the software will function as designed when it goes live. However, this isn't always the case.
It wasn’t all that long ago that you needed a couple semi-trailers and several days to move a computer. Then computers became “portable.” But, they still had four inch low resolution CRT screens that displayed any color you wanted, as long as it was green. Not to mention that they weighed as much as a small safe. Times sure have changed.