Will DMPs be useful post IDFA?

Historical data (pre-iOS14) will presumably be much less useful due to the reduction in IDFA availability. We do not yet know the full extent of the reduction, but it's safe to say that it will be significant. DMPs themselves will therefore be less valuable, in addition to IDFA-based data brokers.

That said, there will still be a need for some type of DMP to store data on people that opt-in via ATT -- not to mention the Android ecosystem -- so there will be some degree of utility for some kind of user-data store, whether it be a DMP or CDP.