A viral infection can quickly become a bacterial infection which should be treated with antibiotics, particularly in the elderly. So for many people it is better to go to the same doc who has your medical record and knows if you are prone to certain complications from an illness (e.g., bacterial sinus infections accompanying a viral cold) or even complications to the treatment to an illness (e.g., allergies to certain meds). The Walmart-style clinic serves a purpose, but it doesn't replace having your own personal doctor who knows your history.
Excellant.
That is a valid concern, however, my mom is not elderly (I'm 22, she's 48 the reason I go with her is because she's deaf).
Even though she has been very prone to needing antibiotics in the past, I carefully watched her and gave her vitamins and good care and she did not end up needing them.
She also carries a full list of her meds and allergies and we make sure to inform the doctor.
Due to her insurance, her specialists and general doctor are 30 miles away and are extremely hard to get in to see, otherwise we might use her doctor more often.
Under the circumstances, with precautions, these clinics are the best many people can do.
Our local hospital complex has an Ergent Care unit in-hospital, and also an Emergency Room. If your doc is not in or it's after hours and you can't wait, you go to Urgent Care. If you are sicker than you thought Urgent Care will admit you or tell you to see your doctor the next day. If it's something that requires an anti-biotic or something like that, then they take care of it. I imagine most hospitals will do this in order to compete with the store clinics.