This seems to be totally totally wrong:
Your database volumes must have at least 25% free space.
The answer is "it depends". You can have 1% free space vs. 50% … depending on the situation and usage, etc. …. there will be no difference.
Other than that, I always would love to have 99% free space. … but it is not a good idea.
Of the biggest problems with SQL Server and giant database tables is that the Statistics is stuck on 200 rows. Hope one day, Microsoft will start using an index param, just like doing asc or descending, you will be able to pick the row or page count for stats.
200 rows works with small and big tables, but when it comes to tables over 10-20 billion … in some cases, good luck.
If anybody from Microsoft wants to contact me on that ….travisGatesMcGee @ Ho tm ail dot com