Stack Ranks / Backlog keeps milestone ends from being death-marches
As a developer, the 'destructive pattern' I see most in software development is when some 'external controller' (e.g. project management, executive management) gets very excited over the fact that 'favorite feature' isn't going to make it on 'calendar date' and orders a death-march.
Scrum, because it ranks 'important features' high in a backlog list helps developers manage this tension proactively in two ways. First, you can rank 'favorite feature' high in the backlog so that s/he is most likely to be happy. Second, it gives a very visual and concrete answer to "since we moved 'blinking widgets' to rank 1, it's very likely that we're not going to get to 'bouncing bunnies' in this sprint since it is now rank 7. Are you comfortable with this trade-off?"
I've also found that with short sprints, 'external controllers' are less upset about postponing work. If 'blinking widgets' doesn't make it into 'milestone 1' and 'milestone 2' doesn't end until 9 months from now, the sponsor of 'blinking widgets' gets very upset. But if 'blinking widgets' is stack ranked 7 instead of 1 because there really are 6 more important things that have to get done first, this means that we'll probably get to it in sprint + 1 or at worst sprint + 2 which means it will show up 12 or 18 weeks from now (using 6 week sprints). In my experience, waiting 3 months is 'acceptable' to the impatient -- besides, back in the 'waterfall' model of 3+ month milestones, waiting until the next two sprints end is the same calendar time as waiting until the current milestone ends.
Finally, if we're reaching the end of the sprint and things took longer than expected, it's very nice to be able to push backlog items 5-6-7 to the next sprint and make sure we've completed 1-2-3-4 with high quality and without 70 hr weeks. After all, we'll be sure to get to 5-6-7 next sprint. Again, given the shorter timeframes involved in the postpone, 'external controllers' are generally more comfortable with this and don't insist that we slip the milestone two weeks and order dinners each night 'to just push through it'.