I typically follow someone in two places only if it is a personal account. For businesses, one is enough. It is tough enough when I follow a business, and then see all the tweets of that business retweeted by everyone else and filling up my stream with something I’ve already seen. I don’t mind cross-posting too much, but if someone is a heavy poster, I probably miss a lot of good stuff because I tend to skim over that person’s content on one platform or the other, figuring I’ve already seen it in the other location.

I think some crossover is OK, but you really need to know who your audience is. I’ve hidden some people on Facebook because their links are of zero interest to me, and that is 90% of what they post.