It's literally in the quote above. It's a potency bonus for any readied combo. Rather than bloating a tooltip with X if A and Y if B, you just use the trait and then use a single Additional Effect. Now you can tune more finely.
Losing F&C+WT has virtually no impact on your ppGCD (especially if you can replace with a spare FT combo or a CT on a new unit), simply because there are few steps left in the combo. Dropping on FT or CT are far, far worse. If we provided a single base bonus for having any combo readied, atop balancing the base potency for level 50 play, dropping before either dragon skill or after True Thrust (2 of 4 GCDs per combo across 58-63 play) would be fine. After gaining Lance Mastery, however, dropping on the 3rd or 5th GCD per combo would each be highly punishing, while the 2nd is made less relatively punishing but still not great. This can be fixed by buffing the effect specifically for the 3rd step and reducing the Lance Mastery bonus onto the second dragon weaponskill slightly (buffing potencies elsewhere). At that point you are punished most on the 2nd and 5th GCDs, less on the 1st, 3rd, and 4th, per combo, but all are within reason. This would leave Dragoon's ranged option as the most flexible and among the most integral, capable of creating different lengths of rotational strings by which to control combo progress at known times of forced melee-downtime.
I already mentioned as much.I said that specifically to point out that while I could certainly throw out ideas for how I think Dragoon's rotation could be more enjoyable, that's not the point of the thread. I gave you a functional Piercing Talon -- hell, one that does allow for a more interesting rotation, coincidentally in giving it pacing control.
If you want a Piercing Talon that somehow suddenly reinvigorates the job in and of itself, despite the thread asking only for a functional one... perhaps you could put forth a suggestion greater than just a chance of free damage or something that desyncs your CDs?