That's a good "division of (stove) labor." JB for warmer weather and water boiling. Kovea Spider for cold weather and real cooking. I often break things out in a similar fashion although I've been using alcohol stoves a lot for good weather solo trips.
The place where something like a JB really shines is when it keeps you from having to bring a second canister. Say you're out on a 4 day trip with a friend. You figure that it'll take about 30g/day of canister gas for two with something like a GigaPower. But with a JB, you can cut it down to 25g (I've gotten by with less than that with a JB). Standard canisters are 110g or 220g. With the JB, I can take a 110g canister and reasonably expect to have enough fuel for 2 people for 4 days. With the Giga, I have to take a larger canister. Not a huge deal, but it is extra weight and bulk to take the larger canister (of course the JB is usually heavier to begin with depending on your pot choice and burner selection).
Also, the JB has some built in wind resistance whereas something like a Giga typically needs an external windscreen.
I'm not knocking or promoting either set up. I'm just trying to throw out some of the variables. I will say that if someone were new to backpacking and didn't want to spend a lot of time trying to dial in their stove system, the JB is a nice option. A newb can pretty much do just as well as a veteran on a JB. (I actually find the JB a little dull -- I mean where's the challenge) :)
Adventures In Stoving