It depends on the amount its discounted for me.
Often in Asda, stuff is discounted but only a small'ish amount. Unless i was buying it anyway, i'd probably pass and buy some in date stuff, plus it depends on the type of food. I never saw heavily discounted food in there at all.
Tescos the other week however, i got three packs of 5% fat mince, should have been £3.50 each....88p yellow stickered

and a large lump of pork i saw several people pick up, inspect and put back. Why ?...it had blood in the bottom of the packaging. £9.80 reduced to £2.30. Brought it, cut in half and straight in the freezer. Had one piece last week, lovely, and only £1.15 for a lump of meat i ended up giving the dog a load of that as well.