the RAW vs. JPEG argument is pretty much the oldest in digital photography and yet it resurfaces every so often.
To sum it up in a short phrase: File size is the least of your problem
JPEG is an image format, RAW is not. RAW is nothing else than a collection of data. The sensor in your camera captures everything it sees and stores it away as RAW, if you decide to use JPEG, the processors throws away everything IT decides is useless including details on shadows and highlights (the +- 2 f/stops gain in RAW is one of the advantages of RAW that you often hear about). There's a lot more than that. RAW is like a negative, you need to process it. JPEG is like the final print. You bring a negative to a photo store and they'll make prints, bring that same negative to 10 different stores and you are likely to see 10 different results because every store uses its own settings. If you use JPEG the processor in your camera will correct light, hue, saturation, etc. based on what it was told when it came out of the manufacturing plant and throw away FOREVER everything else.
RAW processing is non-destructive. If you make modifications today to a RAW file, you can go back 10 years from now and remove those modifications or change them in a non sequential way. JPEG is destructive and sequential: if you change highlights and then saturation and save the image there's no way to go back. before saving you can modify but in reverse order of what you did because a modification changes the actual pixels and therefore previous changes irreparably. Also JPEG is a compressed format with multiple-compression scheme, which means that if you save the image more than once you keep losing quality.
There's a lot more to it but I don't want to get in deeper technical details. Two years ago I stopped shooting in JPEG completely (before I'd shoot RAW+JPEG).
As for Bob's suggestion to delete photos you don't like, as you go, it's a valid suggestion but use some care with it. On my recent trip to Japan I came home and after seeing the photos on my large screen I found out that some of the photos that I didn't originally liked became some of my favorite shots. A camera screen in now way give you the same quality of colors and details of a monitor, before you delete you really want to make sure you don't want that photo. I travel with 12 GB in memory cards (about to grow) plus laptop and external HD for backups. Then again, it all depends how serious you are about your photos.
The way I see it, every photo I don't shoot is a lost chance to make some more money. If you shoot just for fun the game has different rules.
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