Greg and I can always tell if a student has "crammed" their practice into a few hours at the end of their practice week. Often details are overlooked, students are unable to comfortably play their piece under the stress of a lesson, or they have not been able to resolve a problem we have asked them to deal with.
Cramming does not make for good practice. It's great for getting a short term result, but without sustained practice this is only a short term benefit. Students often forget what they have crammed and it becomes a waste of time for the student. And before you ask me is this true? Yes- and there is evidence! According to the BulletProof Musician blog (I'll link at the end of this post), students who spaced their learning outperformed their colleagues who crammed their learning into a single day. the Bullet Proof Musician notes that spaced learning (in our case practice) is more effective because you don't forget as much.
So for our purposes, don't cram practice - space your practice over your week and review what you've practice daily so you don't forget!