There can be multiple reasons for bracketing. For instance, before I started shooting in raw, I would sometimes turn bracketing on because I wasn't confident that I could meter a scene just exactly right and wanted to have some insurance toward getting things right. When I was learning to use the various metering modes, I would use bracketing to help myself learn and understand how each mode worked and how to apply it correctly. Then I discovered HDR photography, and bracketing is a fundamental step in accomplishing that process.

Since I've been using raw to capture and save images, I've not been bracketing nearly as much. It seems to me that HDR works somewhat differently with raw and with JPEGs, and I haven't fully figured out the differences yet in order to get pleasing results. The wider dynamic range available with raw capture seem to make HDR less necessary. Finally, I've not been able to do much railroad photography lately, which is where I seem to encounter my highest dynamic range situations.

A lot of folks here follow a practice called ETTR, or Expose to the Right, which is a way to capture maximum information, usually without having to use bracketing. I've been using a new metering mode called Highlight Weighted Metering, which accomplishes most of ETTR with less work.

To summarize, there are a number of reasons that you might want to bracket your photographic exposures. You just have to figure out whether and why you might want to do so.

I know alot of people feel offended by Bob's quote. I am not. If people do not know how to use manual exposure, then it IS easier to do exposure bracketing and pick the photo with best exposure/capture. I would also add, "or for lazy people or people in a rush." When only 1 photo is truly needed to capture full dynamic range with minimal noise, it is EASIER/FASTER to just do a 3 bracket exposure instead of putting camera on manual mode and adjusting dials accordingly to get the best exposure from 1 shot. I am often guilty of this myself especially if out shooting with a group and have to move quickly. It's not as if we are shooting film. It's easy to delete any unwanted photos while saving the 'keepers'.

Mathematically, each EV stop shifts one bit the sensor readout.

So, in you have a 14 bit sensor, and do +/- 1 EV bracketing, in you will effectively read 16 bit data. If you do +/- 2 EV bracket, you'll end wit 18 bit days and so on.

I've done many sure surveys my line of work, always to find out later that I've missed some important data points. So I've learned the hard way to take as many measurements as possible in the field.

The same applies for photography: get as much data (bracket) as possible, PP later.