I’ve done some testing on this, and I found changing multiple fields with a workflow consumed less unless you are only changing 1 or 2 fields. Each auto-bind will use at least 0.6WU, whereas if you are changing multiple fields in the same Thing, each additional field you are updating on that Thing adds a fractional amount of WU. For example, I have a datatype with about 30 fields. Auto-binding all 30 of these fields would be around 18 WU (0.6WU per field), whereas when I used "Make Changes To A Thing’ and then chose all 30 fields to change, it cost around 3WU for me in this specific example.
Autobinding will cost you more if you’re updating more than 2 fields on the same thing. You’d be better off updating all fields at once. Each autobind cost you the equivalent of make change to a thing… even if all the fields you change are on the same thing.