This little break is ideal for boosting energy and attention. By not entering the REM phase, it will be easier for us to wake up to continue doing things.
Some studies show that sleeping half an hour can cause a kind of sleep inertia. This inertia causes us to wake up with a kind of hangover sensation that will last for about 30 minutes before the regenerative benefits of sleep start to take effect (more energy and attention).
The 60 minute (or one hour) nap is ideal for improving memory of facts, faces and names. It includes the deepest type of sleep that exists (slow wave sleep). The only bad thing about the 60 minute nap is that, as with the half hour nap, you will wake up with a kind of hangover feeling that will not go away for a few minutes.
Napping for 90 minutes is an full sleep cycle. A complete cycle encompasses all phases of sleep, passing through the Rem phase until reaching the dream phase. This nap causes improvements in emotional and procedural memory (eg riding a bicycle, playing the piano ...), and in creativity. A nap of an hour and a half also does not cause sleep inertia (as naps of 30 and 60 minutes do) making it easier for us to get up later.
The vast majority of studies agree that the ideal time for a nap is between 20 and 30 minutes. It is considered that this time is enough to do a light sleep, rest and disconnect from the fast pace of life, so that we can wake up clear and not alter our work schedules.