QUOTE (almost normal @ Oct 23 2012, 02:58 PM)

Just make shit up.
Critical glitch on a dodge, you slip, your helmet falls off, and you expose the top of your head to the gunfire.
Fail glitch on a dodge, the shooters hits become net hits and your armor gets damaged.
I think it's not that hard to come up with situations where downgrading a glitch is better than risking a reroll.
Some GMs will kill an PC if he has a critical glitch in a situation that was dangerous anyway. After all, it's the worst possible outcome of a test that can happen. Many nice GMs will still not do it, but remember that this edge-use-option was written for all player groups and play styles, not only for the ones with nice GMs.
In reality, even a single lucky bullet fired by an untrained (and edgeless) shooter can kill instantly, if it hits the head. In shadowrun the only rule mechanism that can reflect that risk, is a critical glitch on the damage resistance test (or maybe the dodge test). As a GM I use to rule that a critical glitch on a damage resistance test is an instant kill if you dont wear a helmet, but only for NPCs. But some GMs may prefer a grittier game style and rule it this way for PCs too.
If this use of edge isn't usefull in your playstyle, that doesn't mean that it is generally useless.
And remember that NPCs can use edge too. If the barkeeper connection of a PC is hit by a bullet in a shootout, and rolls a critical glitch with his very low damage resistance dicepool, I would rather use the negate-glitch option, so the PC gets a chance to stabilize him before he dies.
But enough of my own rulings. Here are some RAW examples where downgrading a critical glitch instead of risking rerolling is a serious option. Especially if you have a low dicepool.
Climbing:
QUOTE
A character who rolls a critical glitch is in trouble. That character falls with no chance to catch himself and can only be saved by another character, safety equipment, or the good graces of the gamemaster
etiquette and glitches:
QUOTE
If a character rolls a glitch on an Etiquette Test, she’s committed some faux pas that makes her look like a fool—the NPC may be less suspi-cious, but only because she thinks the character’s an idiot and there-fore harmless. If the character gets a critical glitch, the character gives something away that shows she does not fit in, and the level of hostil-ity/suspicion is actually increased by one step (Neutral to Suspicious, Suspicious to Prejudiced, and so on).
Quick Draw:
QUOTE
If he glitches, the gun is stuck in the holster or dropped. On a critical glitch, it is flung across the room or misfired while still in the holster.
Destroying Barriers:
QUOTE
The only way a character could “miss” is if he got a critical glitch on the attack test.
vehicle test glitches:
QUOTE
A glitch on a vehicle test causes something to go wrong with the ve-hicle. This can be anything from accidentally turning on the wipers to getting a flat, at the gamemaster’s discretion. At its most severe, a glitch might cause a temporary loss of control; apply a –2 modifier to tests made by any characters within the vehicle. The driver must succeed in a Vehicle Test within one turn or the vehicle crashes.
If the driver gets a critical glitch on the vehicle test, then the ve-hicle crashes.
Addiction tests:
QUOTE
A glitch result indicates addiction is resisted, but the character suffers a bad experience with the drug (a bad trip, nasty side effects, or something similar). A critical glitch means addiction occurs and the character develops an increased tolerance to the substance.
If you have the "Gremlins" negative quality, glitches may be guaranteed if you reroll (since you need less 1s), so negating the glitch with edge may be your only option.
If a critter uses the "Accident" critter power against you to inflict a glitch or critical glitch, rerolling can often be unlikely to succeed, but using edge to negate or downgrade the glitch will always do the trick.
The same is probably true for the "Gremlins" Power of sprites. (But I don't know much about sprites.)
As you see, many uses for the negate-glitch-with-edge option. No need to forbid the rerolling option to justify its existence.