Those Sell By dates are when the items should be removed from the shelves, almost always perishables - there have been posts about TJs ignoring this many times in the past! Many people are scared by that date, and throw the food out when it reaches it! And that Use By date is much farther away - usually dry goods and canned goods - but some people are still afraid to use it after that!
On the topic of dry goods, through the years I've probably thrown out more dry goods, due to rancidity, than refrigerated items from spoiling. This is something I can smell immediately! Many of the better brands pump N into the bags, to prevent this for much longer, but many things are in paper bags, like flours, of course! And so many have dates on them, but can already be rancid, depending on how it had been stored. A number of whole grain items I have learned to keep in the freezer, along with nuts - cornmeals, cracked wheats and wheat flour (though I usually grind just 3 lbs at a time, to keep in the kitchen), millet, and brown rice can go rancid, if not used often. Since I started doing this, it has been a long time since any got thrown out! Others I have learned will keep indefinitely (though I do vacuum seal them, which helps), along with legumes, which don't seem to turn rancid in storage, though I don't keep soybeans like this.