In today's bitcoin, we know that if you invest with your spare money you may never make any fortune from bitcoin.
Spare money does not mean small money, don't misunderstand the two. Spare money is the money that is not included in your budget for expenses, or money that you budget to invest in bitcoins after you have sorted out other financial problems.
2. Invest what you are able to lose;
3. DYOR (Do your own research):
These two are also still very valid, these are tips that never go out of need and everyone needs to always be reminded about it constantly that is why it is always being mentioned. If they are not said, they will be forgotten and people especially new Investors will make mistakes.
Spare money is as good as investing what we are able to lose. And in the OP's thoughts, Investing into bitcoin with funds that'll be required anytime soon by the investor can lead to losses in bitcoin. Hence, investing in bitcoin for quick profits has nothing to do with spare cash. Like you defined spare cash, if a person invests into bitcoin the money they are able to lose they'll gain enough profits; that should be the reason behind the number 2 advise. Because, they'll consider the investment as a lost money and don't remember to check up on it for a while, given time the money will accumulate to a substantial amount of profits.