Ive never heard that before.....Here I found this from the Yaz site.
Yaz
Its a PDF, on page 12.
Basically, if u miss one, u take it as soon as you remember.. then the next one at its normal time... even if this mean you take 2 in one day.
Only if you miss 2 pills in a row... do you really need to use a back up method. Find Brandye's article called "Take as directed" in this forum section....it explains a lot about what to do if you miss a pill, side effects, and how the pill works.
Yes the pill prevents ovulation, then the days you take the placebo, the hormone levels drop so you can have your period. It also thins the lining of the uterus so that if somehow an egg did make it out, the lining isn't sufficient for implantation or an fertilized egg to grow.... hence why a lot of women have lighter periods.