I always shoot in raw, maximise (quality, size, whatever) the image in PP. I can then make as many jpegs as I want, in which quality I need or want without drama.
Lets remember, that even pro quality memory cards are cheap, when you consider the amount spent on your equipment or the value of the images your taking. Hard drives on computers also don't now break the bank, like in the old days, so get big fast ones, lots of 'em.
What does or does not use the most space type questions, should really not come into it, just bang in another card and get the job done.
In terms of time constraints, the actual time to convert raw to jpeg is next to nothing with modern batch processing that most PP software allows. I get a moments peace, to get a decent coffee while this is going on, then fire the jpegs down the wire.
Therefore IMHO there is no need to shoot both at the same time, but I guess, as always, it's each to their own and what works for you.