Intergalactic Medium (IGM)-based cosmology established itself as a solid cosmological probe with the wide success of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). With the Dark Energy Spectroscopic Instrument (DESI) survey starting imminently, we are taking a look at the accomplishments of SDSS-III with regards to IGM-based cosmology and discussing exciting science and new statistical challenges in the era of DESI.