Maybe for a basic eye exam, but they're also checking for things like glaucoma. Glaucoma in particular is tricky because you may not notice early on, but any damage done to your eyes before treatment is permanent.

In my experience, the cost for glasses/contacts is mostly in actually buying them anyways. Therefore, I just go get my eye exam done and then just buy them online for much cheaper than any retail store. Supposedly the cheap online glasses aren't as good, but they're good enough in my experience and then I don't feel quite so bad when I inevitably lose them somewhere.