Why do they taste so good? This lunchtime, as I was reduced to using the works canteen restaurant, so I thought I would experiment. To make a chip butty you need good chips and a slice or two of bread. White is better as the flavour of wholemeal would interfere with the experiment. You can also do it the Derby way with big floury baps or, as I did, with plain pitta bread. You can spread the bread thinly with butter but it is not necessary if you want the healthy option (Ha! healthy chip butties!) then lay good plump chips tightly in a row before covering with more bread. With the pittas I split them and lined the chips up inside. Despite the wiki article, any sauce is sacrilege. The remaining chips in the bowl (you always get more than enough) form the control.
Now take a good bite and taste. After clearing the palate try an equivalent number of chips straight from the bowl and detect the difference. No bread—but there is more to it than that. What seems to happen is that with plain chips the initial experience is about the outer surface with the oil and salt; with the butty, that is moderated by the bread and the initial experience is with the soft interior of the chip. You still get the crunch on the teeth but you get a fuller flavour. So that is the reason I think.
Available for restaurant criticism on request.