Why are baby bouncy seats unsafe to sleep in?

If this question is referring to a baby sleeping in a bouncer or swing, I've heard that they are unsafe because the babies head can roll forward cutting off or restricting air flow. Charlie was never allowed to sleep in these unless he was napping right next to me in one. If it was bed time and he was asleep we would take him out and put him in the bassinet.

Moms Expertise
    Yes, this is what I have heard too - the positioning can be bad for breathing.
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