More work
As an employee you get "please do this, it will look good on your annual performance review", "or do this, because your colleagues obviously have no problem with it". As an independent freelancer, this is replaced by: "please do this project (more or less) for free, and we will have lots more work in the future".
If you start out new as a freelancer, or if you have hired a few employees yourself, creating a fixed cost base that needs to be filled, this button still can work. But I think for most experienced freelancers with some sort of brand and a large base of existing clients, this does not work anymore. These people probably all work at capacity, and pick projects because they are interesting, push their skill level up, or help out a long standing client even if the work is not interesting.
Filling empty capacity is hardly ever rewarding. SEO, shallow "content" that is pushed on social media. It is better to do great work, get clients excited about you, and get them to refer you to more projects.
I agree that it takes some investment in the beginning. If you are in the early stages of a freelance career, maybe you can suggest to do this project for the full price, but the second one at a discount. The client said she has lots of more work, so that should not be a problem for her.
Art: Marie-Denise Villers, Self-portrait, Young Woman Drawing 1801, Metropolitan Museum of Art.