Lightning is the source for electricity in Miller's experiment.Which means it is the source of electricity for life on earth.
From what I read in Carl Sagan's Cosmos when a chamber filled with gases which are present during earth's early stages and when lightening strikes them molecules capable of yielding life form.
Lightning helps fertilize plants. Our atmosphere consists of approximately 70% nitrogen, but this nitrogen exists in a form that plant life cannot use. Lightning strikes help dissolve this unusable nitrogen in water, which then creates a natural fertilizer that plants can absorb through their roots.
It is also capable of converting nitric oxide into nitrogen dioxide which dissolves in water to form nitric acid.This fertilises plants as said above.
Lightning also produces ozone, a vital gas in our atmosphere that helps shield the planet from rays of harmful ultraviolet sunlight.
