Should I get insoles for my flat feet?

No. It is not necessary to use shoe inserts simply because you have flat feet. Flat feet may be your normal. If you also have foot pain then a medical evaluation from an orthopaedic surgeon would be advisable.
Yes. As the structure slumps closer to flat on the floor, foot function becomes abnormal. The foot will feel more fatigued in the early stages, then develop pain and/or deformities as the altered function causes progressive tissue damage. Proper custom orthotics can alter the biomechanics of your feet which can prevent such damage.
Flat feet . Yes. But i recommend you start with a over the counter orthotic first to see if it helps with any pain than see a local podiatrist to get molded for a custom orthotic.
Only With Pain. Yes , but only with regular sore feet, legs or back. Flatfeet with no discomfort at all require no help at all. And if inserts are not enough, and your doctor agrees that flatfeet are causing pain, then custom made orthotics may help.
Yes. Specialized shoe inserts, such as the superfeet brand, do help persons with flat feet. The inserts have a firm, supportive underside, and a softer foam topside. They help hold up the person's flattened arches.