I don't have "have big useless sum of money laying around", but I keep some altcoins on Binance that worth couple of hundred bucks. I did not earn a lot, but still my money works and I get something. There is a good quote "A penny saved is of more value than a penny paid out.
Martin Luther". That is totally correct about passive income with any amount. Think about it at your leisure.
That means you're stacking on Binance? I hope you also know that you are entrusting your savings there to an unregulated company. It would make more sense to do the staking on a project that is decentralized. There are some good projects here, e.g. Tezos, Waves, Komodo etc, where you can get 5-6% for sure without entrusting this to a central company.