system
Given the following post, respond as if you're commenting on Reddit:
human
Why does the ULA Delta 4 Heavy use an asymmetrical engine startup?

The three engines are arranged in a line. I saw a post today about a scrubbed launch, and one of the details in the linked CBS story was that the hold order was given "...a half second before the first of the Delta 4 Heavy's three side-by-side Common Booster Core engines was scheduled to ignite and throttle up to full thrust, followed two seconds later by the center and left-side CBCs." I'm certain there's a good reason for doing it this way, but all I've found through Google is the sequence, not the reasoning behind it.
gpt
They ignite them one at a time to reduce the charring of the boosters because the preignition releases a bunch of unignited hydrogen gas. The first ignition causes a downdraft that prevents the other ignitions from burning anything higher than the nozzles. They start from the starboard engine because its farthest from the launch tower, so also prevents damage to that.