It's probably for liability, and let's face it... most of the old data terminals were huge. BUT... if your unit says to not leave connected, and in the model, then why take a chance? Even if it doesn't cause interference... the ECU has to sync, and send data to the terminal. That could cause a lag in performance. And finally, you can't look at it while it's flying, so why add the weight, and power draw??

Just my 2 cents... take it for what it's worth.