When it’s time to go to the doctor, getting an appointment can be tough. Many doctor’s offices are only open normal business hours, such as 8 a.m. to 5 p.m., and it can be nearly impossible to get in to see a doctor on short notice. That’s why it can make sense to go to an urgent care facility if you need same-day care for a minor illness or injury.

It’s estimated that about three million people a week go to an urgent care center, and it’s easy to see why. Urgent care centers usually stay open well into the evening, and most are open on weekends. In fact, about 85% of walk-in clinics are open seven days a week. Because of this, urgent care centers can be much more convenient than the regular doctor’s office.

Most people who go to an urgent care center do so because they have a minor illness or injury and they either can’t get in to see their regular doctor or it is after regular hours. Urgent care centers most commonly see people for respiratory conditions such as the cold or flu. On the injury side, the most common issue is a wound that needs to be evaluated for stitches.

People don’t only go to urgent care centers for acute illnesses and injuries, though. Most walk-in clinics also offer routine preventative care such as flu shots and physical exams for children for school and sports activities.

Urgent care clinics have been taking on even larger role in recent years due to a couple of different factors. One is the Affordable Care Act, which allowed millions of additional people to get health insurance. Those people need physicians, and there aren’t enough private practices in most areas to serve those people, so many turn to urgent care centers to fill their needs. Another factor is employer health plans cracking down on the use of emergency rooms by adding surcharges. That creates a financial incentive for people to use urgent care for their emergency medical needs because it is cheaper and they are being forced to share more of the costs.

Whatever the reasons, urgent care centers are playing a much bigger role in health care and are likely to continue to do so due to their convenience and cost advantages.