I use pre-order at other stores, I find it tremendously helpful for coordinating release dates. When you set up the pre-order you get the url/asin/etc all in advance so you can set up your marketing, website, backmatter, etc all in advance and have nothing to worry about on release day. Taking my time 1-2 weeks out and getting everything right is much preferable to rushing around like a headless chicken at the last minute.
Some notes:
1) Rank is impacted at time of pre-order click, not on release day so there is no waterfall effect on rank.
2) You can NOT review a book in advance
3) Sales are credited on release day (as in when you actually get paid)
4) You have to upload a draft to do the pre-order, and the final is 10 days before release. You can set a pre-order just a few days out if you upload the final only.
5) IMO - it is great for getting stuff ready ahead of time (links, back matter, etc) and having the release scheduled so that you don't actually have to do anything on release day.
6) It is great for syncing up the Audio and Ebook release dates
7) it is open to everyone in KDP.
8) If you miss a pre-order date, you are banned from the system for 1 year.
Here is the offical Amazon FAQ:
https://kdp.amazon.com/help?topicId=...B_PREORDER_phl