What opportunities can Substack provide?

If I write tv and movie reviews, for example, what opportunities can that get for me? Can I use that as experience when applying to sites that host reviews? Will that give me more journalism opportunities?

Is it based on quality of my work or is it based on the number of followers or subscribers I have? Or is it based on how viral my posts are or how many likes I get?

What is the ultimate goal beyond Substack?