that's not helpful at all, and pure BULLLLLSHITE..
To help you out flesh, Its not super efficient at your level. You will need to level your Haste and your Flash Das to level 3 before you will reep the benefits.
Once a mob is yellowed it makes a very nice difference. The yellowing is quite RNG, but more often than not, in 1-2 FD's the mob is yellowed.
Once in a blue moon (really rarely) don I manage to kill a PB mob without it being yellowed, I will often FD first get a yellow, half the hp of the mob, then it needs re yellowing.
Its mainly trial and error pal, you will eventually find the sweet spot of when to FD, and then when its no longer required.
In terms of PVP, depending on the class, FD is cruicial. With a wiz/Archer, I very rarely FD as im more likely to just get them down as there health pools are small. Simular to an assassin, but then if they FD you while your Toe to Toe with them, they will win, so again depending on the player its a choice you will need to make. With warriors, your VERY unlikely to kill oe anyway, but if you want to, you will need Yellow up :P
Taos... Well... just run away :P
As I said earlier, its mainly trial and error, and you will start to find your particular sweet spots on when to use it and when not too.
But while lvling, you will want to use this on mobs with a slightly higher health pool.