Really?
I keep my phone in my pocket. With Bluetooth, why do you need to mount it?
To the creator of this thread, I'm sorry you've had to endure this harassment. I hope this behavior isn't typical of this community. It has no place in reasonable discourse.
To: Boxster986S and anyone who has or would post these types of responses. Your comment is off topic, inappropriate, ignorant and judgmental. You're welcome to your opinion, but let's not deride someone for asking the question. Not everyone does things exactly the same way as you. Let me answer your query and educate you as to some reasons why I care about the question which may or may not be shared by this thread's creator. Who knows, maybe you'll change your mind and want a mount of your own.
There are countless reasons why:
First, vehicle navigations are useless. Maps have to be updated manually, In my GLA, I've been sent to countless dead ends and sent on illogical routes into traffic tripling the distance of my travel and wasting even more of my time. The system has 'traffic data' but that's also useless. This data only shows for arbitrarily labeled 'colored' streets. Also, the main reason why I use GPS daily is to know and share my arrival time, and status. I'm trying to be polite to friends, clients, and colleagues. I also want to use my time as efficiently as possible. Modern apps like Waze, Google Maps, and Glympse take care of all of these problems. Maybe the limited data available seems advanced to those who aren't tech savvy, are simply ignorant, don't care as much about their time, or live in cities with little or no traffic. I think most people, or at least the person who placed the initial question don't fall in most of those categories.
Second, let's talk safety. It is unsafe to hold your phone in your phone in your hand or grab it out of your pocket while driving. It's also unsafe to have to constantly look down at your phone, especially while using driving-related applications which may need you to look down to know where you're going. When properly mounted, a phone won't take your eyes off the street any further than looking at the navigation screen.
Third, have you heard of Siri or Google Now? Being able to trigger these functions and see results which are conveyed visibly is priceless. Also, these can place phone calls much more safely than interacting with the car's own systems.
Fourth, you must not use your phone much, or sit in the car for very long. Cell phone batteries are insufficient for almost everyone. I can't know or judge your usage scenario, but 'Keeping your phone in your pocket' while driving is a very bad idea for most people's driving habits. Yes, the car has a USB port, but mounting your phone is a better option for most people.
Fourth, let's talk about Bluetooth signal quality. I can't speak for your use scenario. But, in my experience it's definitely an issue. I always have two cell phones: the latest iPhone Plus, the latest Google Nexus device. I get both the day they come out. This means I have two of the highest-end and best quality devices on the market. If I leave my phone in my pocket, I often have connection issues with the three iPhones and two Nexus devices. This can make music playback annoyingly choppy, or phone conversations rudely cut out. Placing a phone in a mount or in the central area of the car in an open space pretty much eliminates the issue. I've found that traffic, speed, and nearby interference all contribute to this issue. If this isn't a problem for you, lucky you.
There are also countless reasons for wanting this. Frankly, the reason's are none of either of our business. What is your business is to treat the person who posted the initial question with respect. Please be a positive member of this community and don't be a troll.