Putting in discretionary income into your Bitcoin investment dosent automatically guarantee an investor more earning. See ehn Bitcoin is not like some kindd of savings accounts where you keep putting in money without having a clear plan or strategy.
By using your discretionar income for your investment capital, you are safe at least in a way of almost no need of touching your investment capital by need of any regular spendings, bills and even emergencies as you already reserved your income for those things in other financial parts. The investment capital is only from your financial part of discretionary income and after minusing all necessary regular needs.
This investment practice gives you more solid financial foundation that backs your investment more strongly and you don't need to cash out your investment by any regular bills or emergencies. This will help you holding your bitcoin strongly for long-term investment and with Bitcoin, it has been demonstrated by its history that a long time (counted in years) of holding, a better ROI an investor can achieve.
This ROI chart of Bitcoin and other assets with years proves what I said. Use this chart, zoom out like 10 years and get how dominating performance Bitcoin has compares to gold, S&P500 and Long US bond.
https://casebitcoin.com/charts#roi_chart