Depends on their confidence level in signing somebody (Hayward) in free agency
If they feel like they can get him (they probably have an idea of his interest level thru back channels with brad) then you want to use that pick to get another big next to Horford
They really should be drafting a big anyways, but even if they draft at 4 there isn't anyone they can get who wouldn't be a major reach. Markkanen isn't a good fit.