Umm, I'm not sure where these people are getting their information, but I would not suggest doing that. You will end up screwing up your cycle if you keep skipping the placebos.
Why? the placebos are what give you your period. You period is your body essentially cleaning out your uterus etc. You NEED that function. The longer you intentionally miss your period, the more issues you can have. It messes with your hormones, and your health, and can make you physically ill. (nauseous, etc.)
You can skip your period altogether if you really want to. I've done it plenty of times it doesn't really do anything to affect your next cycle. I usually don't even take the placebo ones I just wait for my period to be over (which is like 3-4 days) and then start my new ones.
You don't actually have to take the placebos since they don't do anything. If you have 4 then just don't take anything for 4 days and start your new pack. If you are trying to skip your cycle all together, you can just start your new pack but I would not suggest doing this for a long time.