Your salad example doesn't support your point, it counters it. We can't smell food poisoning, so suggesting that people just sniff the food to see if it's safe to eat is, by your own example something that isn't going to work.
In most cases that extends to using my senses, but if I'd left a bottle of milk outside for a week in summer, I wouldn't sniff it to 'check'.
Also the original comment mentioned best before, not use by. But use by dates are a useful tool, I'm saying you shouldn't just blindly rely on that.
When you sniff food and it smells bad you know that food can't be eaten, so you throw it out. When you sniff food and it doesn't smell bad can that food be eaten? You don't know.
That's why they have the dates: the dates take into account the most common food poisoning bacteria, and best practice storage in the home, and make a balancing act.
What you do with your own body is obviously up to you, but please don't use "I can smell if it's bad" if you're feeding children or old people because they are at risk of death or permanent harm.
The same should apply to food, there have been multiple food poisoning cases in the US stemming from salad, so following best before labels isn't going to avoid all risk. The best option therefore is to evaluate risks for yourself. I don't blindly drink milk based on the date. If it stinks and is lumpy, I don't drink it, regardless of whether it's in date or not.