I've just remembered this thread, as a result of a number of recent research breakthroughs I've had.
I've bothered with the sideways research for a number of reasons (a) you find out more about the nature of the family your ancestor was part of, (b) you can corroborate details about the family especially through the census returns, (c) it increases the likelihood of finding others with similar research interests on Genes Reunited, and (d) there's the thrill of the chase itself!
The corroboration angle is very important. I'd had a lot of trouble tracing any information of substance about the brothers and sisters (and uncles and aunts) of my Great Grandfather Henry Carter. He was born in 1832 in Purleigh, Essex, but had his family in Croydon, where he had a small bakery, from 1871 or earlier. I couldn't work out why he had ended up in Croydon.
I'd identified Henry's siblings and aunts and uncles from the County Archives at Chelmsford, but there was a big gap about what happened to them. I found Henry in 1861 in Aveley, Essex, working as a journeyman Baker. After some patient research of the census's and FreeBMD on Ancestry I slowly pieced together what happened to most of Henry's siblings and his aunts and uncles. Not least he was working for his aunt's husband in Aveley in 1861; one of his sisters and her family was living next door to him in 1871, and that cousins/nephews/nieces moved around between different family members (but not always identified as such) at the times of the census. You can see this pattern at:
http://juliancbaker.rootschat.net/html/24_william_carter2.htm and
http://juliancbaker.rootschat.net/html/12_henry_carter.htmWith a quite common name like Carter these corroborations are really essential. It's not just in this family that this approach has helped. For example the Aunt of Henry's wife had two young children (different surname) as "visitors" with her in the 1871 census, and it now transpires these were second cousins whose mother had just died.
So why did Henry Carter end up in Croydon? It seems that most of his siblings and aunts and uncles also moved away from the Purleigh area, probably to find work in what we now know as the London metropolitan area or the newer towns springing up around it. Also, for Henry and his siblings, his mother had died and his father remarried and moved a few miles away to Maldon - thus breaking the link with the "home" community.
JULIAN