So, you can use
FILLFACTOR to leave space in leaf index pages. Specifying
PAD_INDEX also leaves space in intermediate nodes. What scenarios should you specify
PAD_INDEX, and what benefit does it provide to the index?
From Kimberly Tripp's post:
What she means by high availability is that you don't have the ability to run index maintenance jobs that would lock the table. Personally, I wouldn't recommend ever setting this by default - leave it to DBAs who find that they're unable to manage index maintenance appropriately with any other methods, like using Ola Hallengren's maintenance scripts during off hours. His scripts are genius - they'll do as much as possible online.