Fuel consumption is purely distance based, so going fast or slow will not change how much fuel you use. As for travel time - continous storm riding is the fastest you can go, but if you end up not catching enough storms you lose time because deep hyperspace is very slow.
You only don't use sustained burn when you want to quick-turn (currently you can literally pause the game, toggle sustained burn on and off and it'll reset your speed to zero and let you turn in any directiopn - it's kinda exploity), be stealthy or when you can't use it (when you are under the effect of an interdiction pulse).
Incidentally, it'd be really great if the Sustained Burn toggle persisted through temporary disables. Especially Active Sensor Burst - in 99% of the cases you want to move somewhere after you do a sensor burst, so it permanently toggling off Sustained Burn is just tedious.