It's an important thing to know.
Not only in terms of your style, but in terms of your UI choices.
Let's say you're expecting users to access your content with a phone.
If your target audience includes people over 40, small print (like the login agreement you see when you use free wifi at Starbucks) will create a minor roadblock.
Let's say a fair percentage of your audience may be over 60. If they're logging in with an iPhone, the finger-spread gesture to expand the login so they can read it and tap the button may present a greater roadblock.
Present enough roadblocks, and they'll go somewhere else.
Try walking in their shoes, sure. But also try seeing through their eyes and multitouching with their fingers.
