DaveSSS is correct that the big-big+1" method isn't valid if you ever change the cassette for one with a bigger largest cog. However, I think it's safe to assume you would either fit a new chain with a new cassette or, at least be aware that the old chain wasn't sized for the new cassette.

His little-little method assumes your rear derailleur has the wrap capacity to handle any other gearing changes and I'm not sure that's a always valid assumption either. I tend to violate most rear derailleurs published capacity by substituting 26T grannny ring for the stock 30T on triple road cranks. Setting the chain by small-small would leave me with a chain too short for big-big.