It's advisable not to choose Fast Shot along with Trigger Discipline, as the effects work against each other. Fast Shot multiplies attack speed by 1.2 and accuracy by 0.8, while Trigger Discipline multiplies attack speed by 0.8 and accuracy by 1.2. So you end up with a 4% (= 100% - (100% * 0.8 * 1.2)) decrease of both accuracy and attack speed if both traits are taken.
The bonus to hit in V.A.T.S. is multiplicative, similar to other V.A.T.S. perks, like Sniper and Commando. Taking this trait with Commando/Gunslinger and Sniper will result in a 87.5% bonus to your accuracy in V.A.T.S. for making head shots, nearly double the range of an unmodified shot. The increase is quite significant when compared to the trait Fast Shot, which only results in a 25% increase with all of the above perks.
The trait is best recommended for any play style wishing to be more accurate, such as a marksman, as it can allow for longer ranges of engagement than usual with the added accuracy.
Taken with the perk Ain't Like That Now, the fire rate penalty from Trigger Discipline is reduced from a 20% decrease to a 4% (= 100% - (100% * 0.8 * 1.2)) decrease due to the 20% increased attack speed bonus from the perk.
pcxbox360ps3 When viewed in the GECK, it appears that the AP cost increase of Trigger Discipline affects all weapon types, which is most likely not the intended effect since Fast Shot's AP cost reduction affects guns and energy weapons only.[verified]
pcTrigger Discipline does not affect the rate of fire on fully-automatic weapons. This also applies to Fast Shot.[verified]