There is no advantage to saving anything as a JPEG and it is not a legitimate way to archive RAW files.
There is an advantage, and it's file space. It's your call if this is an advantage to you, but it's very easy to quantify the advantage in megabytes. And no, JPGs are not a way to archive RAW files. They are a way to save images. You missed the point.
You talk about this burden of storing your raw files as if they are a heavy weight you carry on your back everywhere you go. But at the same time you do a double back up AND you leave it on your memory card for a few months ata time? It doesnt make any since.
A bit dramatic perhaps. I do a *single* backup and then leave the memory cards intact until the project is done (usually in a week). The memory card backup (which is on a hard drive) is what I keep for months. And it's "sense."
In 5 years i will be able to buy an external hard drive thats larger than all of the hard drives i have now put together. And i dont really care about cost. If im going to buy a DSLR and concern my self with IQ then i can foot the small sum of cash for a hard drive with several TB of storage and it will hold A LOT of 20MB files.
That's great. Your unlimited cash-flow lends itself well to long-term RAW file storage. My workflow works for my situation, and I wanted to share it to give the perspective of why someone might not care about storing RAW files indefinitely.
I mean hell, while your at it why dont you just convert everything to B&W to get rid of color data and junk the metadata right off the bat to? Why stop at JPEG compression? Lower the resolution as well?
You have to agree that a processed RAW file is very comparable to a good JPG of the same resolution. I would be surprised if you could tell the difference, even at 100% on screen. I don't carelessly trash my images for the sake of file space. I spend a lot of time and effort making them as good as possible. But at some point, everyone needs to make a decision about what to do with a project once it's done. I'm really curious to hear about what other people do.
To the original topic... when I am done post-processing images in Photoshop, I re-import into Aperture as PSD and save these images long-term as JPGs only. So I don't personally use TIFFs (but I used to for years). If a photo did require several layers in Photoshop, I usually backup the layered PSD file for the long-term. I'm sure 40 years from now it won't open. But hopefully it will in 2.