I don't think that the parent means that you shouldn't be structuring your billing to be per hour/day/week of work. Rather, their point is that you shouldn't be doing math like this:

1. "I think I'm worth $75/hr"

2. "the job will take 40 hours"

3. "I'll charge $3000 for it"

but rather, like this:

1. "I think they would be willing to pay me 40k for this, and I think the project should take 40 hours"

3. "Therefore, I'll negotiate for a $1000/hr pay-hourly contract with a projected end-date of two weeks."