It's certainly inconvenient for someone in my situation. Since I'll be walking around a theme park all day in August in FL, I want to dress as comfortably as possible. To me, that means a t-shirt and athletic shorts (they're not super short, by the way). To fulfill the restaurant's guidelines, since I'm staying off-site, I'd need to choose one of a few inconvenient options: (1) carry around fancy clothes all day, (2) pay an extra $8 for a locker on top of the pricey meal, (3) pay for a round-trip uber to shower and change, or (4) dress in less comfortable clothes at the park. A lot of people have mentioned that you can wear slightly nicer clothes to the park to fulfill the requirement, but most of the options they suggest are not as comfy as athletic shorts in my opinion. For some, I'm sure that would be a great option! But I don't want to feel less comfortable all day in order to fulfill a restaurant's (very lenient) dress code for dinner. Especially if I'm going to show up and see a lot of other casually dressed diners, as disneyvoice mentioned she saw at Jiko.
I'm still thinking I'll pack a dress in my bag, but I wanted to address this comment since I've seen a few like it. It CAN be hard to abide by the dress code when you're staying off-site, trying to save money, and wanting to make the most of your time. Especially when nothing's really at stake. They're just clothes!