It helps them in terms of developing their attitude and how they socialize with other people. I personally grew up as the only child for 8 years, and I would say that there is really a difference compared to those peers who have siblings.
For us (my husband and me), para magkaramay sila when they grow old and we are no longer here. Mahirap kasi if solong anak, wala syang ibang masasandalan na immediate family.
Main advantage nyan is lalaki silang close na magiging protector sila ng isa't isa.