The general idea is that you exhaust one market then move to the next. There's a significant amount of people who only read Amazon/KU but not RoyalRoad/Scribblehub and also in reverse. So for web fiction, posting on free sites to build up a Patreon and initial audience is smart, then once you've 'exhausted' that audience (since you get diminishing returns the long your story is on a site like Royalroad, with fewer and fewer new readers), you pull the work, polish it, and put it on Amazon to gain even more readers (these ones who pay passively through page reads, and some of who will also become patrons). This is especially a potent strategy because that already-existing fanbase can help you boost your initial reviews/ratings on Amazon, launching you to the best selling list.
I recommend this guide from TheFirstDefier, who makes 7 digit yearly income on litrpg/web fiction content and knows what he's talking about.
https://www.royalroad.com/forums/thread/116847
Of course, this all depends on the type of serial you're writing. Markets are extremely dependent on the genre you write in.