As long as you aren't depending on this and can easily adapt to going somewhere else and possibly not eating for a while, then go for it. But as a PP said, walking up to a TS restaurant in one of the parks and expecting to get seated is a long shot. In the case of many restaurants, it's futility itself.
If the reason you're asking is that you don't want to or can't make ADRs 60 days in advance, then you have another option, which is to try to book your desired ADR about 24 hours ahead of time or even the morning of the day of so you can pick up on cancellations. This isn't a guarantee, but you'd have better odds than the walking-up method.
Also, you should be aware that even QS requires some preparation since you have to mobile-order now and there are certain places, like Woody's Lunch Box in DHS, that often have a not-insubstantial time gap between the time you order and when you can pick up your food.