Not all photographers are dependent on printing their images or having their image files reproduced in magazines and books (at least not all the time). And all current indicators say that in the future more and more photography will remain digital throughout it’s entire lifespan. In other words I believe that the Internet and other forms of digital media are just as important now and probably will be more important than print production in the future.
Just as an example go to your local news stand and see how many Macintosh magazines you can find (there used to be quite a few), then go online and see how many Macintosh websites there are.
Unfortunately in Lightroom you have to trust the numbers and have no visual means of controling an image for digital output. Fortunately Adobe Photoshop CS does have a Save to Web function that allows you to see exactly (or pretty much exactly) what you are going to get before you post your image to your website or other digital application.
The beauty of the Save For Web tool is that it allows you to see up to four images at one time that all have various degrees of JPEG compression applied to them. Rather than just guessing that Quality 60 will make an OK image at a reasonable size, you can actually see that a TIFF image that was 991K will go down to 83.8K at 60 Quality JPEG and that it will take 31 sec @ 28.8 Kbps to download on the Internet.
If the resulting image looks OK but is too large and too slow, you can try 55 Quality JPEG and see if that still works for you. Go too far down in the compression and you can see the image fall apart right on the screen.
In this variation of the 4-Up screen you can see a comparison between the same image in TIFF, JPEG, GIF, and PNG-8 formats.
In order to use the Save for Web function on images I have developed in Lightroom, I export the image in TIFF or the highest resolution and size JPEG, open up in Photoshop CS, resize that image, apply an unsharp mask filter, and choose Save for Web.