How are HSA accounts useful?

How are HSA accounts useful when the taxpayer has to already have a high-deductible health insurance plan and pays premiums for one plan and is also putting money into an HSA?

HSAs are a new tool to help defray current medical expenses and save tax free for future medical expenses. The accounts are available only to individuals who are covered by a high-deductible health plan.

Funds deposited into the account are deductible and can be invested in individual retirement account (IRA)-type investments. The funds can be used to pay qualified medical expenses, and any unused amounts are rolled forward indefinitely. Any accumulated funds will grow and are not taxed when distributed to pay qualified medical expenses.