nappyadict; sorry, I somewhat abandonned the thread there, having said I found it worked suprisingly well with a 2.4 yo (and no, his understanding is definitely not advanced, and nether is his speech, in fact he's under SALT).
I definitely don't ask why; he's not be able to reply, for a start. But I explain why I need him to do something. So if it's running away in the shops, I'll explain why (eg, just while I pay, look at x, y,z), and tell him that if he can't help himself I'll need to put him in the pushchair/reins. I'll give him a some time to make the decision, and I always give him second chances. Often, second time round he'll do what I need him to. But then when I don't need him to, I allow him to do it his way, and I think it's the balance that counts.
Re getting drseed, this is another one of ours. I'll ask him if he wants to get dressed, often he'll decline once he's stripped to his nappy. I tell that that's OK, but he might get cold, so i'll take some clothes out in case he changes his mind. Usually we don't get out the door before he asks to put his clothes on. Although once it was half way to nursery. the difference between doing this and using it as a punishment/consequence, as I see it, is that when he asks for my help, I give it. The end result is the same; he gets to nursery dressed. When it gets down to it, the order isn't really important.
Maybe this isn't "pure" UC, but I don't think that's what it's about. I take the philosophy, and use it to come up with techniques/methods that suit me and my boy. And no doubt I'll need something different for bump.