It have some effect on lower creatures and bandits.... you can test it in desert.... when attacked by rats you have 5 seconds to run or attack before they start THE attack but when attacked by Enclave or some mutants you are killed immediately when map is loaded.
In TB on "lower" creatures it is good because you can shoot first and got first turn "for free" (sometime if AP is high 10 or more with fast shoot) battle can be finished before it starts.
Mostly it is good for start playing but later it is better to have good armor and good guns and with OUTDOR. and fast run avoid hard encounters.