The idea is that as the loads on the pipeline change, the attendant stresses need somewhere to go; and they often go into expanding the length of the pipe. So the bends et al allow the pipe to flex in without pushing the terminals out of place. And of course the pipe is either hung by flexible hangers or mounted on rollers, like the Alaska pipeline.
So it is in projects: the equivalent to bends and hangers and rollers for pipelines in our business -- see pipelines 1st thoughts in this space a few days ago -- are buffers and allowance for spikes (Agile terminology) where odd things can happen without busting the milestones.
Indeed, every schedule, release plan, budget, and milestone should be buffered so that unplanned debt (again, agile vernacular) has a place to go without putting in peril the whole project. Without reserves, initially unallocated, you've only got a hope and prayer, but not a plan.
