: The time travel mechanic has no apparent story reason for existing. As kind
: of convoluted and screwy as the idea of Cortana encountering a corrupted
: version of herself caused by her own future events is intriguing, it's
: mostly because there didn't seem to be much of a point for throwing
: everyone back in time (it's not even crucial to the Forerunner crystal
: macguffin). If Nylund were on Twitter or somewhere easily accessible I'd
: ask him why it was added. Maybe there were some plans that went awry or
: never materialized.

It is sorta strange. There's an obvious set up at the end for the fragments of the crystal mattering, then it's never come up since. I guess the time travel was used in-story so Blue Team and co didn't have to spend a month stuck on Reach trying to survive, but even Halsey is baffled as to why it sent John back at the perfect time to rescue them.