NEVER defrag an SSD - you may damage it.
Hmmm, well.
I'd rather say ....
"NEVER defrag an SSD because its an utterly pointless waste of time"
Damage is going a bit too far, and likely technically incorrect because it doesn't do anything that a normal of series of reads and writes does.
NEVER use more than 2/3rd capacity of an SSD for maximum performance.
I call absolute BULL on that one.
Its an SSD. You can access all of it at exactly the same speed.
Now, there may be OS related reasons for only using 2/3rds if the SSD is your boot disk (i.e leaving 1/3 free for memory paging etc.)... but that's nothing to do with SSD capabilities.