Take the Weyermann Diastatic Barley Malt Analysis sheet - 300WK = (300 + 16) / 3.5 = 90.3 Lintner
On that same spec sheet it says 'Replaces all or portion of Pale Ale or Pilsner malt'.
Now take the Weyermann Pale Ale Malt Analysis sheet - ?WK = ?Lintner
It's not specified. So how can you compare the Diastatic Barley Malt with the Pale Ale Malt?
You might look at an American Malt with the same name, find that it has a diastatic power of 85 Lintner and use that value for the Weyermann, the alternative is the sac. time, but that doesn't lend itself to determining if you have enough DP available to convert your mash.
Reasons to know the WK/Lintner values:
1.) For apples to apples comparison of grains.
2.) To determine if a malt is self converting Lintner >= 35.
3.) An estimate of the DP power available to convert your mash.
Reasons to relate Sac. Time to WK/Lintner:
1.) WK/Lintner is not always specified on the Malt Analysis Sheet.