Three ways to split, and which one to use
A separate file for each range is the option for chapters, sections or anything where the document is already divided in your head: type 1-3, 4-6, 7-10 and you get three files, each holding those pages in that order.
One file holding every page you list is the option for gathering: type 2, 5, 9 to build a three-page excerpt, or 1-4, 12 to keep a cover and an appendix and drop everything between them. The pages arrive in the order you type them, which is how you can reorder as you extract.
Splitting every N pages is the option for machinery: a 120-page scan cut every 10 pages gives twelve files of ten pages, numbered part-01 to part-12 in the file names so they sort correctly in a folder or an upload dialog.