How will it benefit me?
ISAs are a tax-efficient investment. No tax is payable on any of the income or growth, and you can withdraw money without penalty, unless this is outside the contract terms. A LISA, for example, does incur a penalty if you withdraw the money before age 60, for a purpose other than buying a home.
As ISA allowances cannot be rolled over, if you don’t use your allowance by 5th April, it will be lost. That’s a potential £20,000 reduction in your tax-efficient investment pot.