When I talk about guaranteed contracts, I'm not really speaking of the money - it's the years. That's what makes it so painful for a team to actually let some players go - or makes it impossible to trade them. An older player with 4 guaranteed years at a minimum salary of one million, for example.
When the contract is guaranteed, the coach and the management has lost a significant amount of leverage. Not that it's either bad or good - I certainly see the players' perspective in this as well - but it can make motivating a player more difficult.