I'm not sure where the word "allow" comes from. I didn't say anything about anyone granting anyone permission. Nor did I say that you should tell your players anything. I talked about what I "need", meaning what I am looking and hoping for, out of play.Yes, I've occasionally had long shopping trips. I don't "allow" it in any sense because I don't intervene in what the players are doing as long as I don't believe they are simply misunderstanding something. As far as shopping for outfits? The players were having a blast, why would I tell my players that the fun they were having was wrong?
If my friends want to play-act among themselves shopping for finery that is of course their prerogative, but it's not something I really care to spend my leisure time participating in.
Again, I don't know where this language of "stop" comes from. I'm talking about what I do or don't enjoy, and what I do or don't look for in RPGing.But as @robertsconley eloquently pointed out above it does point out quite clearly that you are exercising a great deal of control on what the players do and putting your thumb on the flow of the game when you stop no-stakes colorful-in-character narration.
To set up a comparison: I speak no Greek, and so I would get little pleasure from participating in a RPG session where all the other participants are speaking in Greek. But I never have occasion to stop my friends from playing RPGs using Greek as the principal language of communication, because as it happens they all, like me, default to English as their preferred language.
Similarly, I've seen no sign over the decades that I have been playing RPGs with them that they are inclined to spend tens of minutes settling on the cut and colour of their PCs' finery.