Since Adobe’s Lightroom and most of the other tools that I use are geared towards DSLRs, I have felt the need to add as much EXIF data to my scanned images as possible. The more photos I add to Lightroom, the more important Smart Collections are getting to me and the less I want to rely on keywords. Things got even more complicated when I started using more than one film camera and wanted to use the standard ways to sort my photos by camera. Besides, I do have a blog and display my photos online, it is rather normal that my visitors want to inspect the EXIF data to understand how I arrived at this particular exposure, what my reasoning was.
Luckily, my Pentax MZ-S and Pentax 645NII cameras record exposure data on the side of the negative, but even if your camera doesn’t do this, it is still worth adding at least the camera information, film information, development information, used ISO, and any other thing that you can remember to the image. I use Vuescan to scan my negatives and it would be a great if this tool could also store all the EXIF you have available, but unfortunately it only stores the minimum EXIF data in the scanned image. I suggested adding EXIF data functionality to the image to Vuescan but I guess that Vuescan is already complicated enough and it never was added.
If you have googled how to update EXIF data in an image, you have probably come across the ExifTool by Phil Harvey. This tool can do everything and more, but in the end it is a Perl script with a command line interface. What was needed was a graphical user interface to the ExifTool and Bogdan Hrastnik has stepped up and developed the ExifToolGUI Windows tool for which you can find all information here. Strongly recommended!