For example, an NT child would know that you go into a shop, you choose an item, you queue to pay and then you can leave. If you are spending too long choosing, the NT child can say 'I'm bored, can we go now?' or 'it's too noisy in here'.
A child with ASD might have no clue how long they have to stay in, what happens next, how many processes have to be completed before they can get out of the hell that they have been brought into.
Add to all of that the likeliness that they will be more sensitive to the discomfort of the situation.
A solution could be a)to make a safe place in a pram under a blanket with ear defenders. It could be to b) take them into noisy places for a few seconds building it up with rewards for sticking it out. It could be c) a social story or visual timetable that explains the usual routine in a busy shop with a very clearly marked END.
I prefer the last two together b) and c) as they move towards socially acceptable behaviour and functionality, and I prefer not to go straight to a). But, there will be times when only a) will do and exercises to enable the child to access a) I think is really important, just not the starting place.