when the engine is revved hard, there's definitely significant movement and the flex sections accommodate this movement. i think the envy chargepipe would be under a lot of stress all the time if there is no flex section present. i would be afraid of cracking that could occur on the charge pipe due to prolonged fatigue over time.
however, this of course is just my opinion, i have yet to see or read a thread where a charge pipe did indeed crack.
Current: 2013 F10 M5 & 2013 GLK350
997.1 GT3RS (gone)
2009 WRX STI (gone)
e92 M3 (gone)