the "Metering Timer" in Live View (40D)

Does anyone understand the advantages and disadvantages of the particular settings on the Live View's metering timer?

The manual says with the metering timer "you can change how long the metered exposure setting is to be retained."

The 40D Guide to Digital Photography says the metering timer "determines how long the 40D continues to measure exposure..."

Is this function basically an AE lock for Live View? The camera will use the metered exposure setting for every shot taken within the timer's setting? I don't think that's right, but I can't come up with anything better. I've set the timer to all of its settings and haven't noticed anything different...

Thanks in advance for any thoughts you'd care to share.