Let the carbon build up. It's seasoning and food doesn't stick to it.
Just preheat the grill to burn off any remains from the prior use. If there's really heavy buildup, use a straight edge scraper like a paint scraper or heavy spatula.
Cleaning a grill down to shiny bare metal is a sure way to have all your food stick to it every time.
Grease and oils get rancid, particularly in hot weather, and rancid grease on the grates can make your food taste bad. Rancid grease on the bottom of the grates can vaporize and flavor the food, too.
The black crust on the grates is mostly carbon. It tastes bad. In addition carbon insulates the grates and can stick to food. So it is vital that your food go on clean grates.
I think that part of the disparity is in frequency of use: if you cook on a daily (restaurant) or even weekly (enthusiast) schedule, you won't have problems. If you only grill on major holidays, you won't be able to just use it without cleaning.
Also, a grooved scraper with the right spacing for your grate does a great job of removing large chunks. You don't need to polish it to bare metal, just remove that excess. Scrape after grilling while it's hot, wait a week, wipe with a paper towel dipped in olive oil when it warms up, and it works well enough for me.
Incidentally, the occasional griller is also the exact person who would most likely be least aware of the danger with a wire brush... sort of a perfect storm situation
You can do it with a pellet grill/bbq too; most of them can get a grate temperature well above 500 degrees, which will do the job. Not as good as propane of course, but easier than charcoal or wood.
Because I don't want my meat to be covered in the ashes, the burnt food particles add bad flavors, ash-covered food looks unappealing, burning off hanging chunks of fat causes excess smoke, and ash-covered food is more difficult to visually measure doneness.
Pre-oiling your metal grates should be done to prevent sticking and burning off excess food particles should be done to prevent build-up.
It's pretty much exactly like seasoning a cast iron pan -- get the grill grates screaming hot, switch off the heat, sop up a paper towel in your high-heat oil of choice (eg: canola oil) but not dripping, and wipe your grill grates.
This is generally only possible with a cleaned grill and it would be prudent to clean your grill after it's heated up and before you apply oil.
Cheese dripping from cheeseburgers or heavily sauced ribs can leave a mess, which can smoke/flameup and give newly cooked food a bad taste. Normally I just brush enough to get the big stuff off the grate.
Or you could just clean it with old wooden utensils that are on their way out, or slice an onion in half and push it up and down the grill with a wooden spoon.
I have also always subscribed to the "Al Bundy" school of grill-cleaning.
The loose carbon also makes it easier to make the "grill marks" that prove "this item was cooked on a hot grill" without actually burning them in too far. This is important if you actually cooked the food by some other means and only used the grill for Maillard, caramelization, drying, and the cosmetic grill lines.
If I'm in there to actually cook something, there's usually a foil packet involved, because otherwise one needs a humidity reservoir, or some other means of retaining moisture in the food, and the tasty fats still drip out.
Not sure if that was a joke, but since it's the internet I'm obligated to take it seriously. :p
That burnt gook always tastes bitter to me. The flavor of BBQ is primarily Maillard reactions of proteins and carbs reacting, aromatic phenols from herbs and spices, and polyphenols from wood smoke.
When you cook fat and meat such as a BBQ polycyclic aromatic hydrocarbons(PAH) form and those compounds contain several benzene ring molecules. Part of the Maillard reaction process is the creation of PAHs. It's part of the process when cooking meat but not the only thing you taste. PAHs are used as a food additive "liquid smoke" to add a smokey, sweet flavour.
Let the carbon build up. It's seasoning and food doesn't stick to it.
Just preheat the grill to burn off any remains from the prior use. If there's really heavy buildup, use a straight edge scraper like a paint scraper or heavy spatula.
Cleaning a grill down to shiny bare metal is a sure way to have all your food stick to it every time.