Well i just googled it and got about 20 different answers, all the same opinion I might add

It's this simple. The manufacturer has stated the car needs this tyre. The reason is the XL tyre can take more load. You have to take into account this covers high speed and high speed cornering under loaded weight not just people in your car or luggage etc.
Standard tyre's are about 35psi on average and the XL 40psi+, Obviosuly from that you can tell it will carry more weight more safely.
Take this example. You buy non XL tyre's. As a one off you ferry 4 people and luggage to the Airport. Driving along you hit a pothole and because you don't have the XL tyre to take the impact of all that weight, your tyre's blows and you crash..... ( bit sombre but plausable).
Cops come along check your tyre's (assuming they notice) and carry you busted up car and body off to somewhere safe. If they've noted the tyre's on the inspection that's it your insurance is void and you'll get nothing, simply because you didn't follow the manufacturers guidelines. Why would you even risk it tbh ?
I know this as I've ordered non XL tyre's for my Mondeo (now replaced with a golf

). The fitters refused to fit the tyre's because they we're not suitable for the car. They ordered the correct XL's and i returned the next day, a little embarrased
