It's not about can or can't, you don't get the point.
It's about safety measure (that's the point of designing), and by measure, you prevent stuff from happening before it's too late.
You can't tell perhaps because you don't ride it hard enough, or just cruise casually on good flat pavement. When you attack the twisty mountain roads with potholes things can get ugly if your chassis isn't stiff enough. And when shit happens it's reassuring to know your setup is stiff enough to not flex and slings your man-bike center of gravity the wrong way.
If you lose grip or or corner too wide because your CoG is messed up during a tight turn, that's life or death situation. That may sound extreme, but that's how some of us ride, and part of the thrill (and a different story). But to take it to the (reasonable) limits, you need to have it set up and prepared the right way.
So, whether you ride it casually or ride it like you stole it, a stiffer chassis is always a plus, because it is less likely to surprise you in a bad way when shit happens.
But it's your bike, do what you like.
