I love the marked down section, and my favorite grocery store is Grocery Outlet, where many things are sold because they are closer to the expiration date, or the box may have changed ("regular" stores don't want to keep selling the Christmas package in March, even if the food doesn't expire for a year).
Recently I found pints of cream for 25 cents each. I bought 5 and wish I'd bought more (I put some in the freezer and made butter with some). A week ago I got half gallons of milk for 80 cents (good for a week after the date if unopened). After Christmas, the same store was getting rid of eggnog, so that was down to $1 for a half gallon.
I don't do dented cans though.
At one time, a lot of it was necessity. I no longer have the need to purchase food this way, but why not enjoy the savings if I can use the food and not waste it, especially if it is something I'm going to buy anyway?