This 'effect' was very handy in Descent
, where you could engage both forward and side thrusters at the same time, making your effective speed equal to the hypotenuse
of the two perpendicular speeds (sqrt(2)=~1.4142) - approx. 41.42% faster than with just the forward thrusters.
Once you had the 'leet chording skills necessary, you could combine this with the vertical thrusters as well, giving you a ~73% speed increase. Throw in the afterburner power-up (which doubled forward speed) and you really could rev that ol' gunship up. You had a very vague idea where you were going, but hey, it looked slick.