It's all about using your time and money to do as much good as possible by some objective measure. It falls apart completely if you don't share the objectivist perspective thought. From a nihilistic POV, I would argue these measures don't really matter at all. In my personal opinion, it's better to do something that feels important to you personally (both with your time and your money).

That said, I do heavily recommend giving https://80000hours.org/ a look regarding this topic. They are not all about effective alturism, but it is a key part of their work. Their career guide touches on basically all important parts of it, and I think it gives genuinely good advise and some interesting perspectives.

I do buy that at least the authors are actually serious about doing something good here, obviously I have moved past some of their notions thought.