Maybe in an exp party where you're going to be engaging and disengaging constantly.
What does this have to do with it?
Not to mention you're already getting a sufficient amount of DA in other places.
Only ~20% at most, assuming /war. Also, there is no "sufficient" amount of DA; it just becomes slightly less effective as you stack more.
I did some math to show you:
Assuming a base delay of 1 second per swing (for ease of math; The base delay does not really matter).
with 50% DW: 0.5s
with 24.6% haste: 0.377s
with 25% haste: 0.375s
with 39.6% haste: 0.302s
with 40% haste: 0.300s
with 59.6% haste: 0.202s
with 60% haste: 0.200s (-80% delay; capped)
after 60 seconds of attacking:
24.6% -> 159.15 attacks; with 23% DA -> 195.75 attacks
25% -> 160 attacks; with 20% DA -> 192 attacks
39.6% -> 198.6755 attacks; with 23% DA -> 244.37 attacks
40% -> 200 attacks; with 20% DA -> 240 attacks
59.6% -> 297.03 attacks; with 23% DA -> 365.35 attacks
60% -> 300 attacks; with 20% DA -> 360 attacks
In both Non-hasted and Hasted situations, 3% DA beats the .4% haste.