I can see and I can smell, so no I don't bother with them but I know some people without a brain who follow them to the letter and throw food out as soon as it's only one day past the use by date. It's one of the biggest causes of food waste.
It is all dependant on what the food happens to be, obviously it makes sense to throw away stale and mouldy old bread, while hanging on to mouldy old cheese.