In reply to SARS:
Cheers for confirming my guess. I'll look at it again then. I still think the risk of causing someone to fall off by not paying out fast enough has to be weighed up against the chance of someone falling while they;re pullling slack up - most of us usually fall while we're clipping, if we're gonna fall clipping.
If always wondered if the original petzl method (regular belaying - like putting your seat belt on while your cornering at full petzl) was developed at crags with really long routes wiht a lot of unobstructed air to fall into.
I've certainly often observed the competition wall style of belaying safely using a Gri-Gri - stand 4m back from the wall and have a marvellous 1m deep catenary of slack. Indeed, it does keep you off the deck if you fall clipping the lower off.
My final thought is, I've held falls recently off trad routes and they're hard to hold, just box standard ATC and 8-9mm rope. I'm not saying I'm in competent - noone's decked with me belaying - I'm saying (in single pitch safe climbing when you lower off and top rope or bring up a second) the grip position of your hands used in holding a fall is the same as what you were just using a minute ago while you pushed your self to your limit. You are not always as fresh ready to go fully compus mentis belayer with all devices as you would like to think you are. For now I'm tempted to try sticking an extra gate in the ATC. Given my grip is tired, I wonder, am I really safer belaying with an ATC than a Gri-Gri (and using a single rope instead)? - I've always said it's Petzls' next logical development to make a double rope version of the Gri Gri - just sticking two cams either side of the current rigid bit in the midle and having two flappy bits. but then you could be looking at a £100 belay device that only one portion of UK climbers will buy, and another will decry as black magic and the devil's work.
I may choose to ignore other belay devices in this post. Hardly anyone uses them for a reason. Except the Reverso and Italian hitch.