Not sure what you're asking. If you don't want to add extra affects, you don't have to.
In the case we're talking about, it has to do with the Light Property. The Light Property allows you to make an off hand attack as a bonus action if you are wielding two Light weapons. So, a lvl 5 Fighter would have two attacks as part of his Attack action, and one attack as a bonus action with the off hand. Just like 2014 DND.
If you have the weapon Mastery over a weapon that grants Nick, then the Nick Weapon Mastery allows you to make the bonus action attack granted by the Light Property and makes it a part of the Attack Action. So that same Fighter, if he were using a scimitar and had Mastery over it, would make three attacks as part of his Attack Action, and still have a bonus action to use on something else.
And that's where the Dual Wielding Feat comes in. It allows a SEPERATE Bonus Action attack, distinct from the one granted by the Light Property. So if you have mastery over Scimitar's, and are wielding two weapons, That same Fighter can then make 3 attacks as part of their action and another one with their bonus action.
Most classes don't get Masteries, however. Just predominantly martial ones, unless they take a Feat.