I'm not sure about Buffet's advice, but John Bogle (founder of Vanguard) recommends bonds so that you can rebalance your portfolio to your desired asset allocat

I'm not sure about Buffet's advice, but John Bogle (founder of Vanguard) recommends bonds so that you can rebalance your portfolio to your desired asset allocation when stocks are down by simply selling some bonds to free up capital. So if you have 90% stocks and 10% bonds but the market takes a dive and now you're at 80%/20%, you can sell enough bonds to bring you back to a 10% bond allocation and use those funds to buy more stocks.