honestly i, based on my own experience as well as my own knowledge on programming in general recommend not doing this; at least not automatically.
i and i'm sure plenty of others have been stung by lazy or incompetent devs/publishers/etc pushing out patches that fix 3 problems but create 5 more possibly even worse bugs in implementing the workarounds to fix the first 3.
good (read as safe) practice in pretty much any software that patches is to not automatically update and instead (unless you actually currently have an issue that you cant fix yourself with the software) wait at minimum 3 or 4 days before applying a patch just to see if there are any reports of severe issues once its been push out to the wild.
if there are no reports of it completely taking a dump on the software then i'd go ahead and apply the patch.
but you know, just this programmer's 2 cents....
[Edited by Mechcondrid, 5/22/2017 9:31:10 PM]
Steam removed like a decade ago the possibility to opt-out of automatic updates for installed games. The things you can do now is to stay offline, set restrictions to the download time and bandwidth, allow/prevent downloads during gameplay, always keep a game updated, only update it when a game is launched or always auto-update it.