You can get by in life without a vehicle diagnostic tool, so long as you have a buddy nearby who can help reset faults and or diagnose codes... but if you can afford it, it's super handy to have with you at all times. That's probably the single reason that I like the VAD Mobile
concept over the VAG-COM version that requires a computer. With a simple (and cheap) Palm Pilot purchased from eBay, I am able to get OBD-II information immediately when I need it. Compared to the VAG, it is admittedly missing the simpler "long coding" features and
the ability to sample at a super-high rate, but those features in my opinion are outweighed by the convenience afforded by the portable Palm Pilot based VAD. The bluetooth connection is a plus for me, however I originally only upgraded because my previous cable version is not compatible with the MKV's CAN system. That said, I must admit that I am enjoying the faster connection speed and convenience of a wireless system. The only downside is that the wired version used to keep my Palm fully charged at all times, but I now remedy that by charging the Palm in the car on the way to the track.
I especially enjoy the ability to monitor real-time information when out on a track day. When I had my MKIV R32 with the HPA turbo kit, I always monitored coolant temps at the track along with intake air temps (IAT) because the car's built in coolant gauge is worthless since
it only moves once temps are way passed normal operating temps. Keeping an eye on IAT versus ambient temps is also cool to note the efficiency of the intercooler, and this is especially true on HPA turbo'd cars since they relocate the IAT sensor from the MAF to the
intake manifold, so it's reading after the turbo and intercooler.
With the MKV, since we have an OEM oil temp sender, I now monitor oil temps on the track and even in my current NA form, was able to see that my oil temps hit a unsafe high of 286 degrees at WSIR in 96 degree ambient temperatures. This informs me that the car
is not built for tough track abuse at the factory and as a result, I've started work on putting the pieces together for an oil cooler kit that is optimized for track use.