It's very situational.  I've been sorting through clients and I have a chunk of clients that are in or beyond the phase-out (so their CTC for 2021 will likely still be $2K/child which we're already adjusting for via W-4 box 3).  If they already get the extra $2K via reduced withholding AND now a $1K advance, they're going to have a balance due.  Mostly I'm trying to avoid the "why didn't you tell me this was going to happen" situations.