For example, if you control The Ozolith ("Whenever a creature you control leaves the battlefield, if it had counters on it, put those counters on The Ozolith.") when Sin's last ability resolves, you'll put the appropriate number of each kind of counter onto both The Ozolith and the target creature
Besieged Viking Villages abilities can give you +1/+1 counters, while chaos lets you put an indestructible counter on one of your creatures
Its removal both early and late, and its also excellent reach for closing out a game
With them you trade a bit of mana efficiency over one mana burn for some card efficiency (lower burn per mana but more burn per card)
On top of the solid body, the death trigger that cares about your nontoken creatures provides a huge creature advantage in your hand
Unlimited Edition made a number of aesthetic changes to the face of the cards