I understand the FAN concept of genealogical research (research the friends, associates, and neighbors of your ancestors–great idea!). But I think that researching the 4th cousin of your 2nd cousin’s great-grandmother (on the other side of the family) is a bit much. The same thing goes for the guy who tells me he “knows everything about my grandma” because she’s his ex-wife’s third step-mother’s tenth cousin.
I have much closer relatives (ancestors, aunts/uncles, first cousins of ancestors) for whom there are original records I have not yet accessed, databases I’ve not mined completely, etc. I’m going to focus on them because their stories need to be researched and told.
And in many cases, researching their FAN network is essential. That’s especially true in areas where there are few records and every clue that one can dig up can help paint a more complete overall picture.