Many people who take a year long sabbatical, do so from summer to summer, so that they have 2 low income years. This brings you in a low income tax bracket, so that every hour you work gives you more nett income than in a normal year.
With a lower income, you might be eligible for paying lower fees, or for subsidized health insurance? But I expect this to be mostly for people with very low incomes.
In my country, we have to pay 30% taxes for taking out profit of the stock market from a taxed account. If income is zero, or under a certain minimum limit, that is a good year to take out such a profit.