Say I give you an intermediate descent: "Descend when ready FL310, expect FL250 by LOGAN". This will be against other traffic. If I then step you down in stages to FL250, I would expect you to make FL250 by LOGAN without me NEEDING to restate it every time. You were given the restriction in the first clearance.
But an 'expected level' isn't a restriction so you haven't actually given the pilot one
