Well Cody and I just got back from a GREAT wedding in Cullman, Alabama. The groom's father and step-mother are professional photographers and old friends, so it truly was an honor to be a part of their AMAZING day.
When teaching Cody and I are ALWAYS asked (and even a time or two here on the forum) how do we or what do we meter when using TTL off camera lighting. So I wanted to show everyone the evolution of how we capture an image and how the below image took only two shots to capture without any light meter or manual light settings. All happened in a matter of about 10-15 seconds to capture usable image.
Fast - Effective - Portable - pretty much what we do all the time, hope it helps a little on how we capture our wedding images.
This image is my "Light Check" or "Light Meter" image - I simply and roughly pose the subjects where I want them, set my camera and wireless flash to what I think is needed then take the image.
Shutter Speed: 1/1000 of a second
f/stop: f/5.6 (due to the large group otherwise I would have shot at f/2.8)
Lens: Canon 15mm fisheye
Body: Canon 30D (yes my older but goody still works great)
Camera Mode: AV (A for Nikon People)
Metering Mode: Spot - metered on the grooms face being that is the key to the image
ISO: 125
Flash: +1 on the flash comp.
As you can see the sky is not where I want it - it is blown out somewhat and the light on the grooms face is too bright. So taking these factors to mind I made the following adjustments to the camera and flash settings, fine tuned the groomsmen to fill the image out as I saw it in my view finder then took the next image, which is Straight out of the Camera completely with no Photoshop or retouching on it.
Shutter Speed: 1/2000 of a second - removing ambient light therefore bringing in the clouds better, however STILL METERING ON THE SUBJECT NOT THE SKY
f/stop: f/5.6 - left it alone only change the shutter speed makes things easier and faster to adjust
ISO: 125
Flash: -1/3 on the flash comp.
Then wanting to edge it up some - yeah I might have gone a little far but you know what I love it and judging by the groom's face on the SOOC version and then watching him get excited when I told him what I wanted to do with the image I think he will enjoy this version as well. Of course the key is the SOOC image is strong so you can do anything you need to the image from basic retouching to edgy beyond this example.

Oh I removed the Fish effect using Photoshop if anyone was wondering why the two look slightly different.
The advantage of TTL metering is once you understand it you simply can get strong images faster than manually metering all on the go in a very fast paced situation of weddings and even other photography subjects such as Seniors/Grads, Children, Animals.
Hope it helps just trying to spread the love of TTL wireless flash metering :) heheheheh