JS_Harris - 1:49 am on Jul 18, 2013 (gmt 0)
By having many sites try to rank for any given keyword you increase your chance of landing top billing and mitigate your risk of a Google change taking out your "only" site. It's a good tactic in a crazy and ever changing Google algorithm, unfortunately. It makes sense, the reasoning to do it is sound and with no sign of Google "tremors" slowing down at all it's the smart thing to do as a webmaster moving forward.
When will it be safe to focus on one site exclusively again? I don't know, perhaps when Google stops making 2-3 changes per day. Can you imagine watching a football game if the field and rules changed 500 times a season and the teams are not informed?