Are there any disadvantages of not to letting baby have a pacifier? Like affect their brain development?

Don't think there are any disadvantages. It's also a matter of choice whether you choose to give baby the pacifier.

I have 3 boys age 10yr, 7yr and 1yr. Never need to intro pacifier as it was never a need

No, only for their teeth growning will be not very straight and nice.

I won't use one, but if you do it needs to be taken away by age two.

My brain works fine.. I eat pacifier till at least 5yo.. Hahaha

My daughter didn't experience any pacifiers. She's smart.

No but it can help if your worried about SIDS happening.

Not really but as some say it helps them self soothe :)

Not at all, some babies don't like pacifiers

I think no disadvantages