The oldest galaxies that have red shifted off the spectrum and are only visible with this. You can’t do IR telescoping except at L2 because earth is giving off its own IR reflection or radiation or something like that

Hopefully it'll tell us about the period of reionisation, when the light of the first galaxies made the universe transparent again.

It should be able to detect the atmospheric makeup of expo planets (via spectroscopy during a transition). This will let scientists search for signs of life on other planets.