The rationale is that at least part of each sleep episode is during the circadian period when sleep is expected. Anchor sleep is a technique used during ones shift off during a series of nights. It is basically a compromise to switching to a diurnal orientation. One would stay up until 3 or 4 am and then sleep until 10 or 11. That way one gets some time to socialize but doesn't completely lose a nocturnal orientation.
Naps are problematic.
Regularly scheduled naps can be effective and some industries with multiple workers on night shifts include them in their shift design. Pharmacology must also be considered. Sedative hypnotics should not be routinely used by night workers. They are very addictive, and while they do increase total sleep time during the day, they do not hasten resetting of rhythms to night shifts or improve alertness during the night. Caffeine is nearly universally used by shift workers.