​Does size matter?

Here is the deal: sometimes i see how some of web novel authors are planning size of their books to be over 1 mil characters per volume, or kind of. I dont know how and why, but i guess thats not normal.

I see the size of a book as something that combines compactness and spaciousness, at least a volume. But i personally whouldnt even start reading a fictional novel, which has over 1000 pages.