I followed a Jaime Oliver recipe for curry, which started with grating onion, ginger and garlic. I liked the curry, but grating an onion is a miserable job. He said that technique unlocked the onion's 'sweetness'. How much difference do you think I'd notice if I used a food processor?
A food processor will do a very similar job, some food processors even have a grating accessory you can buy. I wouldn't worry about the modest difference in flavour.
The more you cut an onion, the more cell walls you bust open, releasing more flavor. Grating works well for this, but a food processor will do a fairly good job, as would a grinder or mortar and pestle.
When I make curry, I usually just dice the onion, though, unless it's supposed to be particularly onion forward, then I'm going to be using the mortar and pestle.
depending on how fine you took it in the food processsor, the only difference is the crying.
what 'unlocks the sweetness' in onions is being cut or otherwise mashed very finely so it more or less melts into the food. (the finer it is, the more 'melty' it gets.) it's similar to garlic and other aromatics in that respect; and it doesn't really quite matter how you get there.
I would not suggest huffing the bowl when you're done, though. Unless... you know. I won't judge.
Not to mention, but the lachrymator is fairly unstable, and its pungency won't last nearly as long when the onion has been pulverized. Bigger pieces hang onto their alliinases, and, unless you cook those bigger pieces a lot, when you bite them, you'll get that onion crying smelly flavor.
Jamie Oliver does terrible things to a LOT of recipes. Remember when he tried to "enhance" a Tandoori chicken recipe and called it literally "Empire Chicken"?
Cut it coarsely. As you cook them, add a tiny bit of sodium bicarbonate. After they melted down, add a tiny bit of vinegar to neutralise the bicarbonate.