When and where were your brothers and sisters born? Did they marry? Have Families? (Follow up for the details) What were they like? Do you have any favorite memories of them?
The important element of identifying the location of birth for the siblings is to put together the migration pattern of the family. In my own family my grandmothers family moved from Northwest Ohio, Northeast Indiana, Northeast Ohio and then finally to Southeastern Michigan. The motivation was the time period and the constant need to find employment. In this situation it was not driven by family already being located in the area. Each of my G Aunt's and Uncle's was born in a different location. Meeting their spouses all along the way.
The importance of marriage is when you are looking to trace the siblings lines. Learning about these families help in understanding the fabric of the family.
Understanding more about siblings helps in understanding more about your own family line. This to me is what makes genealogy fun.