This is useful when cutting cards by hand: even if your cut is slightly off, you won't see a white edge
The more interesting application of gold borders came with the 1996 Pro Tour Collector Set
Kazandu Mammoth / Kazandu Valley Kazandu Mammoth is a beefy creature played in stompy decks, and together with fetch lands, you can have a 7/7 attacking on turn 4
Frodo, Adventurous Hobbit, Mentor of the Meek, Lobelia, Defender of Bag End, Savvy Hunter, The Gaffer, Night's Whisper, Harmonize, Trading Post, Well of Lost Dreams, Dawn of Hope 10 card draw
Savannah Lions (T1, Ext, S) The best offensive one-drop creature in Magic history, hands down
If the spell you cast has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost