Digital Photo Format

[AliBaba]

A file in RAW-format has all innformation from the camera. It's smaller then TIFF (even if it has more data) because it is compressed.
A JPG is compressed and a lot of information is removed. Sometimes it might be hard to see the difference when you look on the picture on a monitor but if you try to adjust something (colorbalance, levels, contrast) you will see that the result is far better on RAW then on a JPG.
JPG is optimized to have all the data you can see with current adjustments.
If you print the picture you can normally spot which one is in RAW.
Okay, you might say that you don't adjust your pictures but your software does (viewers and printers) so in the end you will loose on JPG. Unless it's only for web-use and stuff like that.

For printing 300 DPI looks to be the rule. That means that 3000*2000 will give yo 10*6,6 but often you can stretch it a bit.
8*10 means 2400*3000 but it's smart to go higher because then you have room to crop the picture.

Yes, the files are large (tiff 2400*3000 is 20MB).
When I scan my negatives (for magazines) I use 5232*7800, that's 117 MB TIFF, that means that the pitures from my Africa-trip would have been 137GB or 240 CDs.... Wonder why I used film?

You have payed for the pixels, use them.
If it's possible store in RAW. When you have made your adjustments then it's okay to store them in JPG but keep the original RAW-files.

Compression kills details, it's an efficient way to lower the quality on your shots. It's like putting smaller jets in your carbs to lower fuel consumption :-)

If you want lower res or pictures with low quality buy a cheap camera, not a Nikon D100.