Because it might get all mouldy and you can get sick, sometimes its still eatable before its out of date but its your choice to take the risk to eat it or not it depend what it is and how it looks :)
A lot of foods have a best by date. Usually all of the food in cans, bottles, boxes, and bags have a best by date. Food that doesn't have something protecting over it like fruit and vegetables doesn't have a best by date usually.
In most circumstances, yes, you can. The best before date simply means that after that date, the food may begin to lose quality.
If it smells ok, looks ok and you cook it at a high enough temperature it should be fine- food doesn't know it has a best before date people are way to wary nowadays
the use by date is that is advised to be eaten by... this does not mean to say that is has to be eaten if it is fine if it going moldy it is rotten so throw it away :)
The "best by" date on food products indicates the date until which the product is expected to be at its best quality, while the "use by" date is the date by which the product should be consumed for safety reasons.
"Best before Jan 2010" indicates that the food product is expected to maintain its best quality, flavor, and nutritional value until January 2010. It does not mean the food is unsafe to consume after that date, but it may not be at its optimal quality. Always check for any signs of spoilage, such as off smells or changes in texture, before consuming food past its best before date.
Best before dates deal mainly with taste and performance, not food safety. For example, a cake mix that is beyond its "best before" date may not taste as good or may not rise as well. The cake, however, is fine to eat. I've never had a problem with a product consumed (well) after its best before date. Expiration dates tend to be more on refrigerated foods and should be consumed within a week or less after the date.
Centres which sell or give away food past it's best before date
mostly a week or two weeks before it expires
A "sell by" date means after this date the store should not be selling the food, at least not at full retail price. There is a window of time after the sell-by date before the food is spoiled.
because you might get sick from it. the food might be rotten after the expiry date and also, it wuldnt be as delicious as the taste before the expiry date
There should be a 'best by' date on the bottom of the container. Quality will not be guaranteed past that date.