Do you like reading in bed? Chances are, you love it. You're a writer, so you're probably a reader, too. If not, why are you here?
I like to read a chapter or two before I go off to sleep. It's great for taking my mind off the niggles of the day. I don't care how long the chapters are, there. I read a page... I read the next page, I turn the page. All the pages are the same size and contain the same number of words. Can you imagine what it would be like if each page was lengthened to accommodate the number of words in the chapter. How inconvenient would that be? You'd have pages a yard or two long, and would probably lose interest by the time you'd reached the fifth paragraph, and wouid throw the book onto the bedroom floor in disgust.
That is the closest analogy I can find for what it is like to read on screen. You scroll down the page until the end of the chapter. If you have to scroll for too long, something in your "reading muscle" says, I've had enough. I'll come back to this later, and you page mark it, but when you come back - IF you come back - you have to find the place you left off reading. With a book, if you start to feel sleepy mid-chapter, you can put a bookmark between the pages. Here, you can only mark the whole chapter.
When you write a chapter or branch here, have a look, before you hit the publish button. Imagine yourself in the reader's seat. Would you have the stamina to plod on to the end? If the answer is no, then it perhaps needs to be broken up into two, or even three, chapters.
For me, anything up to around 2,000 words at a time is just about my comfort and attention limit for on-screen reading. It may be more or less than that for others.
Another thing about reading online, is that, if you do not use line breaks between paragraphs, your beautifully crafted prose turns into just a block of text, which blurs, and hurts the eyes, and makes the reader want to go and read something else instead. It probably looks wonderful in Times New Roman 12 point, with the paras marked by indents, but the text is so tiny here, that we have to accommodate that, by switching to line breaks instead.