A very vague one. Bold is a bit stronger than italics, plus italics are overloaded, they are used to signify other things than emphasis, too. In the grandparent post there are both italics and bold because the emphasis is somewhat different so I wanted two different ways to emphasize.
Completely off-topic, but do you have a policy for when you emphasise with italics and when you emphasise with bold?
A very vague one. Bold is a bit stronger than italics, plus italics are overloaded, they are used to signify other things than emphasis, too. In the grandparent post there are both italics and bold because the emphasis is somewhat different so I wanted two different ways to emphasize.