One advantage I see is that you can use the Tip to give your engine an "Italian Tune-up". I have heard that the DFI engines will build up carbon/sludge faster if you run them in the very low RPMs. Tip allows me to get the maximum RPMs before shifting and the car sounds great as well.

 

Any restrictions on changing between the three modes (D, S, Tiptronic)?
I mean, is it OK to change between these while car is in motion, or is there
any max speed below which it is safe to do so, etc.

Have always changed modes after bringing the car to a stop ...

 

as far as i know there shouldnt be a problem with switching modes while moving. iv gone from auto to tip while moving quite a few times and there are no problems. when you switch like that the car just stays in the current gear.
however, if you go from D to S the car should/may shift gears depending on the speed, which shouldnt be a problem unless you do it excessively or stupidly, but that goes for just about anything lol