ZFSTuningGuide, MySQL on ZFS, zfs set sync=disabled question

[Dmitriy Makarov]

Hello,

reading https://wiki.freebsd.org/ZFSTuningGuide I found the tweak

* zfs set sync=disabled tank/db

but no tip/note/info about this decision, or warning.

Googling about disabling sync with MySQL got results with strong and reasonable advice do *not* disabling sync for databases like

http://list.zfsonlinux.org/pipermail/zfs-discuss/2015-February/021132.html
https://wiki.archlinux.org/index.php/ZFS#Database  ("never disable sync for a database!")

FreeBSD wiki recommended to sync=disable, is it related with some of FreeBSD ZFS extra-feature which is not present in other OS ZFS implementations?
Is it totally safe disabling sync for heavy loaded databases (for InnoDB-only MySQL), what side effects can occur (common and worst case) and why?

Thank You for detailed answer!