Best practices for applying sharpening in your workflow

Question

Recently I have been trying to get a better understanding of some of the best practices for sharpening in a workflow.  I guess I didn't realize it but there are multiple places to apply sharpening.  Which are best?  Are they additive?
My typical workflow involves capturing an image with a professional digital SLR in either RAW or JPEG or both, importing into Lightroom and exporting to a JPEG file for screen or printing both lab and local. 
There are three places in this workflow to add sharpening.  In the SLR, manually in Lightroom and during the export to a JPEG file or printing directly from Lightroom
It is my understanding that sharpening is not added to RAW images even if you have added sharpening in your SLR.  However sharpening will be added to JPEG’s by the camera. 
Back to my question, is it best to add sharpening in the SLR, manually in Lightroom or wait until you export or output to your final JPEG file or printer.  And are the effects additive?  If I add sharpening in all three places am I probably over sharpening?

Answer 1

You should treat the two file types differently. RAW data never has any sharpening applied by the camera, only jpegs. Sharpening is often considered in a workflow where there are three steps (See here for a founding article about this idea).
I. A capture sharpening step that corrects for the loss of sharp detail due to the Bayer array and the antialias filter and sometimes the lens or diffraction.
II. A creative sharpening step where certain details in the image are "highlighted" by sharpening (think eyelashes on a model's face), and
III. output sharpening, where you correct for loss of sharpness due to scaling/resampling or for the properties of the output medium (like blurring due to the way a printing process works, or blurring due to the way an LCD screen lays out its pixels).
All three of these are implemented in Lightroom. I. and II. are essential and should basically always be performed. II. is up to your creative spirits. I. is the sharpening you see in the develop panel. You should zoom in at 1:1 and optimize the parameters. The default parameters are OK but fairly conservative. Usually you can increase the mask value a little so that you're not sharpening noise and play with the other three sliders. Jeff Schewe gives an overview of a simple strategy for finding optimal parameters here. This is for ACR, but the principle is the same. Most photos will benefit from a little optimization. Don't overdo it, but just correct for the softness at 1:1.
Step II as I said, is not essential but it can be done using the local adjustment brush, or you can go to Photoshop for this. Step III is however very essential. This is done in the export panel, the print panel, or the web panel. You cannot really preview these things (especially the print-directed sharpening) and it will take a little experimentation to see what you like.
For jpeg, the sharpening is already done in the camera. You might add a little extra capture sharpening in some cases, or simply lower the sharpening in camera and then have more control in post, but usually it is best to leave it alone. Step II and III, however, are still necessary.