Your employer will continue to pay you wages if you fall ill as an employee, but usually only for 42 days. As a privately insured person, you should take out private daily sickness benefit insurance in order to financially secure a long-term illness.
If you are self-employed, you can also agree on an earlier date for payment of the daily sickness benefit. This can be of existential importance, as income is often missing at the beginning of the illness.
It is up to you how much daily sickness benefit you wish to insure. However, it may not be higher than your net income from your professional activity. Your average earnings over the last 12 months are taken into account. You should therefore always report a permanent reduction in your income to your daily sickness benefit insurance.