Most photographers try to plan their concepts out in detail for quite a few reasons. It could be time, it could be financial, or it could be as simple as not wanting to look inept in front of a client. In any case, there always seems to be something that could be just a little bit better. In some cases, like this example, a photo conference had some models posing with some basic sets and lighting.
OK, the subject is reasonably well lit, and has sort of a dramatic look about him. But what if you wanted a few different looks with this subject, perhaps with a little more separation from the background? That may be your vision, but perhaps not the 10 other people in line wanting to make a pic of this subject. Once you get home there is a pretty quick and easy way to get a little separation only using Lightroom (or camera raw in photoshop).
Grab your radial gradient tool and increase the exposure by quite a bit. We now have a separation light on the background, but the subject's face is very overexposed.
With the radial mask still selected, Choose Subtract...subject.
The subject is now subtracted from the mask, and the separation light still remains behind him. You still increase or decrease the luminosity of the light, or even change the color of the light behind him if you wish. While this may not be as ideal as if a strobe was actually in place, a little experimentation with this technique can go a long way. Give it a try the next time you want just a little extra in one of your images.