The spacing effect is a psychology term that refers to the fact that one can learn and remember items in a list more easily when they are studied a few times over a long period of time, rather than repeatedly in a short period time. The spacing effect was first identified by Hermann Ebbinghaus in 1885.
The way this phenomenon relates to studying is that, it suggests that "cramming" the night before an exam is not as effective for learning and retaining material as studying at shorter intervals over a much longer span of time.
However, there is no benefit to spaced presentations (studying a few times over a long period of time) for retaining things for short periods of time. At short retention intervals, massed presentations (studying repeatedly in a short period of time) lead to better memory performance than spaced presentations.
So basically, the spacing effect proves what you already know. If you really want to learn something, you need to really study it. Review the material in short intervals over a long period of time. If you don't care about learning the material and all you want to do is pass your test, by all means cram away. It actually works better in the short term.
