That's feels like it should make a difference, but it doesn't actually offer any additional damage. The sim has lines using Blood Tap to maximize Soul Reaper uptime and it simply does not matter. You comment those action lines out and the numbers don't change.
The posts talking about burst are technically true, but you can only hold Blood Charges for ~4s before you cap them, and it's only 2 runes. I find that argument unconvincing for PvE DPS.
For most PvE DPS DKs, in most situations, if you choose Blood Tap you should macro it into your runic power spender.