Proven to reduce the incidence of respiratory distress syndrome (RDS) due to surfactant deficiency.
Meta-analysis shows benefit even for babies near term ie 34-39/40! Risk ratio 0.74.
Not much data on long term outcomes, of course, but RDS rates high even at 38 weeks so LSCS should not be planned until 39 weeks.
Repeat courses of antenatal steroids (due to threatened delivery) associated with lower birth weight, so should ideally be limited to 3. [https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1002771]