Still gives you negotiating leverage, but just in a different way.

Doing all the grungy work means that a.) you can describe what grungy work needs to be done that a potential new employer and b.) you can describe the solutions you took to these problems. Basically, you can pass all the bullshit filters that savvy employers put in place, because you are not actually bullshitting.

You still make your money in the transaction, that point where you actually get an offer letter from an employer and negotiate a compensation package. But the input to that compensation package is based on how much value your new employer expects you to add to them, and a primary input to that is how much value you added for your past employer, and how much your new employer believes your claims of that.