Using an equity ISA can help to maximise your investment returns because you can avoid any tax liability on the returns you receive. For the same reason, cash ISAs can offer a more competitive alternative to regular savings accounts.
A combination of equity and cash ISAs can help to spread the risk of your investment, so that some is protected from fluctuations in the stock market, while the rest can have some exposure to risk for potentially higher returns.
Equity investments and the income from them can fall as well as rise in value.