Example: If I buy a lotion and it says "Factor 30 light protection: Protects from sunburn and skin cancer" then I must be able to rely on that. I mean, If I want to go to the beach then I need a good sun lotion to protect my skin. If it doesn't work I'll have a serious health risk. So it is totally correct that the state makes it be illegal to write that sentence on any lotion that does not protect your skin from sunburn and skin cancer.
Other example: If an electric iron says it has "safety motion sensors" that will switch it off if you do not move it for 3 minutes, then careful people will still plug it out before leaving it. But a person who relies on technology may think that the device can remain plugged in. So they just go away after ironing their shirts and then if the promised feature does not work - it may be setting the house on fire.
Well products costs money, and we purchase products for their function. Therefore, its important to know if products work so that we don't waste money..? Not much point buying products that don't work.
You're able to ascertain whether or not you're 'wasting' your money !!