Sequences in XSLT 2.0..

XSLT 2.0 has introduced a major paradigm shift from XSLT 1.0 by
introducing the concept of sequences. Now everything is a sequence.
Earlier everything was a node-set. I wonder what was the need of such
a major change? What does sequences concept achieve that node-sets
cannot? Why was it considered neccessary to introduce in XSLT 2.0?

I'll appreciate if somebody could explain the rationale behind sequences..

Best regards,

Weinberg's Second Law: 
If builders built buildings the way programmers wrote programs, then
the first woodpecker that came along would destroy civilization.