You pay less for covered in-network health care, even before you meet your deductible.
Having a health insurance can lower your costs even when you haven't met your deductible. Insurance companies negotiate the cost of service with providers, so you pay a discounted rate.
This means that when you use an in-network provider, or a doctor your insurance company has negotiated with, you pay less for the same services than someone who doesn't have insurance.
So even if you don't reach your deductible during the year, you can save a lot of money on your covered medical services just by being enrolled in an insurance plan.