Why are 'saved as' .psd files so much bigger than original raw nef files?

Question

I was under the impression that original raw files were the biggest possible. I appear to be very wrong. Why are 'saved as' .psd files so much bigger than original raw nef files?
I'm beginning to think that saving them as psd is a bad idea.
Yes, though I've heard all the arguments of keepng the original raw files (For ex. Did you throw away the negatives when you were using film) I se eno purpose in keeping them. Once I've made the initial adjustments--cropping, color correction etc. I don't feel a need to ever go back and never do. Most of my work is done in Photoshop and I like it that way--but suddenly finding myself with such huge files doesn't appeal to me at all--and other formats like tif...well never mind for now.

Answer 1

Good point made c.pfaffenbichler however, my thinking is this--there is time spent on the raw file and then there is much more time spent on (usually a psd) the file once in Photoshop. For me to then go back to the orignal raw file, after having worked on it on PS would mean getting rid of all the work (larger amount of work, time wise and artistic wise) done on PS which seems pointless. Although the psd file does show your layers and stuff it only shows the end results of that layer. It does not show from where to where you pointed your brush, from what point to what point you changed the color or part of an image etc. etc.Anyhow I understand why most people keep their raw files, but this is the main reason why I do not. It would mean hours of work on an image you already worked on (and usually were satisfied with) to perhaps make some minor alteration. Also please note that though I was noce a pro photog, no I do it mostly for fun. Getting the exact red in my Coca Cola can has never been of importance. On the other hand, if there were a way of working on a raw file within Photoshop and keep it (save it as) a raw file equivalent, then I would absolutely do so.