Price of dreams

Many years ago, I came across this phrase: dream as much as you can, because it won’t cost you a thing. But is that really true?

When I fall in love, I can spend hours or days fantasizing about our future together.
When I get a job offer, I imagine how I’ll reach the top of my career there in a few years.
When a project brings in its first $100, I’m already thinking about how I’ll make millions from it.

I can spend a lot of time dreaming and get lost in memories of the future. And this can hinder my productivity.

If dreams take up so much time, do they really cost nothing?
And in that case, which is better, to dream or not to dream?