Grand and formal - reserved for historic figures, generals, founders, statesmen. Using it for ordinary achievements sounds sarcastic or ironic. Common in eulogies, commemorations, and textbooks.
grammar
Parallel coordinate structure: 丰功 (abundant achievements) + 伟绩 (great feats). Both halves mean essentially the same thing, doubled for rhetorical weight. Compare 千方百计, 字斟句酌.
