Every photo can benefit from a bit of sharpening, specially photos shot in RAW format. All photographers out there already know that sharpening should be your last step in your workflow. As a matter of fact it is there in Lightroom's Export feature for a reason. The question remains however: what is the difference between Sharpening and Clarity in Adobe Lightroom?
In Lightroom, there are two places to sharpen your photos. The first one is a slider in the Details section of the Develop module, and the second is an output sharpening option in your Export functionality. Both however should be applied at the end of the develop workflow and there is a reason for that. Well, this is why; sharpening works on the edges of light and dark pixels. The algorithm is build to look at lines of pixels in your photo and to lighten the pixels next to light lines, and darken pixels next to dark lines, thus creating a better definition along these edges. Notice below subtle difference between left and right pictures.
Clarity on the other hand adds contrast to the mid-tones of the photo. The results is in the details of the textures. Clarity also results in lesser noise to the photo than sharpening. This is why the sharpening slider is immediately positioned before the noise reduction slider in the workflow. Notice the details in the walls between both photos below (click to enlarge).
Adobe improved Clarity big time since version 3 where if you would cranked it up more than 30 it will introduce artifacts. In version 5+ the whole algorithm has been improved and the result is amazing every time. Whenever I have textures I depend more on Clarity rather than Sharpening. As a rule whenever I have architecture, landscape and textures in my photos I tend to increase clarity and whenever I have portraits and people, I tend to reduce clarity and increase sharpness a bit.
Remember though no to boost them a lot and to uncheck the sharpening checkbox in the export option if you have already done so in the develop setting.