Basic foam pads—simple EPS or EVA foam with a thin fabric cover—provide adequate cushioning and get the job done for short, casual rides. If you're a commuter with a quick 15-minute trip or a weekend cruiser who rides in mild weather, they'll likely feel fine.
The real downside is moisture management. Basic pads absorb sweat poorly and aren't removable for washing, so they can get grimy and uncomfortable on hot days or during longer efforts. Once that foam starts holding odor, there's not much you can do about it short of replacing the whole helmet.
If you ride regularly, in warm weather, or for more than an hour at a time, stepping up to removable, washable pads is worth it. But if you're on a tight budget and mostly doing short, easy rides, a helmet with basic foam pads still protects your head—which is what matters most.