This means that the cap, near the start of the mRNA, is near the subunits of the ribosome when they disssociate at the end of translation. If they are so nearby, then it is likely that they can quickly reassemble and start again to transcribe that mRNA, saving time that would otherwise be taken as the parts diffused in from elsewhere.
Work Step by Step
For an analogy, imagine that you are cooking hamburgers on a grill. You fill the grill, but you keep the box of uncooked burgers on the left side of the grill so that you can quickly refill it once the first set of hamburgers is cooked. The hamburgers are like the polypeptide, and gripping the cap and tail near one another on the ribosome is like keeping the box of uncooked burgers nearby for the next round of grilling.