Consolidation might prevent citizens from over collecting welfare benefits.
Another reason why the Democrats will fight this with everything they have. You can bet that Trump will demand that the consolidated agency put in place systems to verify that each recipient is (A) a citizen, and (B) eligible, and (C) not collecting benefits under multiple identities.
If I were doing it, I would have each recipient have to prove identity in order to get benefits, and then give the verified recipient a biometric picture ID card. That way, it would be harder to claim that demanding ID "disenfranchises the poor".