I'd be interested to hear how large your files are - RAW, JPEG, whatever.
I often hear of enormous files, but other than saving as TIFF, I'm nor clear how one would get there.
In Photoshop you can increase the size of a file by interpolation, that is adding pixels, to increase the size of the original image. The results depend on the algorithm used. Algorithms are based on a mathematical formula which can be quite involved to produce the best results. For example if you think of a red box made of nine pixels, to increase the size of it, you would add 16 red pixels around the original box, so increasing the size of the box to 25 pixels and by so doing, you have also increased the size of the file. When you do interpolation it degrades the image so you need to apply sharping to make it look less blurry.
As a general rule you can increase the size of an image in Photoshop by six times without degrading an image to much. So, if you increase the image from A3 to A2 it can look fine unless you look at it up close, but generally you would stand further back to view the A2 image than a A3, so this blurriness would be so noticeable.
My D700 will take RAW and RAW lossless compressed. The RAW files are usually around 24MB the lossless compressed around 14MB.
I'm a bit confused as to how the files can be "lossless" when they are 10MB smaller....
Converting a 24MB RAW file in ACR at the largest setting (6144 x 4088) at 400 ppi still "only" gives me a JPEG file of around 10 MB.
Maybe I'm just having a blond moment ...
If you take a landscape shot with a blue sky then, in the original Raw file each pixel of the sky is recorded separately for colour and position in the original Raw file. By using a special algorithm it can record the position of the pixels, but as the colour in the blue sky is the same, it can just record that colour in one place and apply it to all the other pixels in the sky rather than for each individual pixels, so reducing the size of the original file.
The Jpeg file algorithm has greater compression than a Raw file compression, it also throws away information that it doesn't need, so reducing the size of the original file. The problem with this is you have no control of what information it discards so the image is degraded. This is the reason why you shouldn't keep saving a Jpeg file. Having said that you would be hard pressed to notice the difference between a original Raw file and when it's saved as a Jpeg. Hope this answers you questions.