Dark energy is best known as the putative agent of cosmic acceleration--an unidentified substance that exerts a kind of antigravity force on the universe as a whole.
Less well known is that dark energy also has secondary effects on material within the universe. It helped to imprint the characteristic filigree pattern of matter on large scales. On a smaller scale, it appears to have choked off the growth of galaxy clusters some six billion years ago.
On a still smaller scale, dark energy has reduced the rate at which galaxies yank on, bang into and merge with one another. Such interactions shape galaxies. Had dark energy been weaker or stronger, the Milky Way might have had a lower star formation rate, so the heavy elements that constitute our planet might never have been synthesized.