Two recent articles point out that the prevailing notion that an eight hour chunk of sleep is required for optimum health and function is a relatively recent invention that doesn't take into account the usefulness of many varieties of sleep. Randall notes historical and contemporary evidence that other patterns are useful, and here is an abstract from Dewar et al. on how wakeful rest enhances long term consolidation of new memories:
A brief wakeful rest after new verbal learning enhances memory for several minutes. In the research reported here, we explored the possibility of extending this rest-induced memory enhancement over much longer periods. Participants were presented with two stories; one story was followed by a 10-min period of wakeful resting, and the other was followed by a 10-min period during which participants played a spot-the-difference game. In Experiment 1, wakeful resting led to significant enhancement of memory after a 15- to 30-min period and also after 7 days. In Experiment 2, this striking enhancement of memory 7 days after learning was demonstrated even when no retrievals were imposed in the interim. The degree to which people can remember prose after 7 days is significantly affected by the cognitive activity that they engage in shortly after new learning takes place. We propose that wakeful resting after new learning allows new memory traces to be consolidated better and hence to be retained for much longer.