If I only did direct lineage I'd only have a list of names, dates, g.stones etc but because I have siblings of my gran done I've learnt a lot of stuff from them and their descendants, been shown/given photos, told stories etc
When I went looking around area my g g/father lived I got talking to some local farmers, when asked who my g g/father was I was told there were 3 by that name but because I knew names of his 6 siblings they knew which one I was looking for, even took me to meet a 102 year old man who knew him!!
Also, took someone looking for kin to the area her kin lived, she was told there were 3 Marys with same Surname that lived in area, one had a brother and sister, another 1 brother and 2 sisters and the 3rd had 2 sisters and 3 brothers..... because she didn't research siblings she/they couldn't identify her family! The locals knew the history of the 3 families but because she didn't know siblings had to leave empty handed...