It is not a “slight” reduction in emissions, it’s absolutely huge! About half of the aviation industry’s total impact on global warming is due to contrails! This is 1-2% of all human caused warming across all industries.

(Though slight caveat for any nit-pickers. The warming isn’t related to emissions. The contrails essentially create a blanket that traps heat in the earth’s atmosphere - the BBC article linked mentions this)

Source: https://youtu.be/QoOVqQ5sa08

(Or check the sources in the linked video)