My favourite boy's name is 'Reuben', but for reasons of family history I have really bad associations with the name 'Ben'. Do you think a child called Reuben would get abbreviated to 'Ben' once he's in school? At home we could call him 'Rube' for short but I know, from teacher friends, that once they get into school they often get nicknamed to the more obvious shortening.
If he was likely to end up being called 'Ben' I would rather not name him Reuben, that's how much I hate the associations of that name (apols to all parents of Bens - nothing against the name itself, just the person it makes me think of)