BTW, when you save an image that you've edited in Photoshop, which format should you use? PSD or other?
Can where you save lead to disorganization of your file storage or external HD back-up...which I think I managed somehow !!
The key here is to save your file in an uncompressed format whether it be as a PSD or TIFF (with layers preserved). This will serve as your "master" file from which you can print, resize for electronic viewing or emailing, etc. These additional versions you'll want to "save as" so as NOT to overwrite your master file.
As to where to save your files, use whatever folder hierarchy makes sense to you.

For instance, my hierarchy is based on "shoots" and I've designated specific drives for photos only. Inside of each "shoot" folder are the original images (sorted by date shot), then one folder for "masters", one folder for resized "JPGs 5x7 at 96ppi" for emailing, etc. I keyword them so that if I want to find every frame I've ever shot of say a bear (or more generally, mammal), I can find them quickly. I also fill in data fields such as location, copyright, among other things. Adding notes to a shoot or to individual photo files are very helpful as well, for instance "this pupfish population is genetically isolated".
Using your organizing software with a hierachy that works for you will make reviewing and later, finding a specific image(s), easier and more enjoyable.

The neat thing too is that you can always revise your folder scheme so don't feel like it's got to be perfect from the get go. You can always fine tune it as you go.