I thought you had it too. ; )
Think maybe how you worded things. Continuous is main stream all the time. As
@wittaj said, continuous+triggered records the substream until a trigger, then records main stream. Yes, if you used a higher quality substream then you'd have something a little better even if you're viewing the substream. But that will cost you a little more space. Still much less than the main stream.
Just to further confuse you, you can set different cams to work in different ways so could go continuous on a primary cam and when triggered on a cam that's not so important.