From the debian release notes for Jessie:
Jessie ships with systemd-sysv as default init system. This package is installed automatically on upgrades.
It then details steps you can take to prevent systemd-sysv from being installed but with the note
(!) Caution Be advised that some packages may have degraded behavior or may be lacking features under a non-default init system.
I read that as saying while you don't have to use systemd, don't expect everything to work if you don't. And once things stop working, the choice pretty much goes away. It's not FUD, that's where it looks like things are headed.