This just landed on the master branch.
Starting with LibreOffice 3.5, you can now specify the initial number of sheets that new documents will have. Previously, this was hard-coded to be 3 sheets in all cases no matter what. While this didn’t seem to bother a whole lot of people based on how little bug reports we’d received on this, it did bother some users enough so that one of them have decided to code up a patch to make it happen. Now, without further ado, let’s take a look at the new option page:
where you can change the number of worksheets in new document, which becomes effective the next time you create a new document.
Last but not least, the name of the person who made this all happen is Albert Thuswaldner. Please give kudos to him for his excellent work. :-)