system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] Why did the Forerunners design the Halo array to be fired more than once?

Why would they ever want the Halo array to be fired again. The only reason they did it the first time was because they had indexed the galaxy so they could reseed it, but there wouldn't be an index safe aboard the ark to reseed it a second time if they are fired again. Was it just a fallback murder suicide incase the flood rises again, ensuring that if life can't win, then the flood can't either? Why only allow humans to turn it on then? 

And now I think, can they be fired more than once? The monitor seems to think it can, but the only ring that actually fires in the series was made after the first firing. We see in Halo 2 and 3 that they press the big button to fire, but it never fires.
gpt
There was always a chance that the Flood may someday return. There are situations where the Halo Array may be worth firing, even in the absence of a reseeding program.

The Array only destroys intelligent life. Once activated, there's always the chance that new intelligent beings could evolve. But if the Flood wins, then that's all there will ever be. The Flood will be the only life that exists in the galaxy, forever.