I am typically the the type of person who always waits on iOS updates. I want to be sure every last bug is worked out. The last thing I want is an unusable, or "bricked", iOS device. However, iOS 9.3.5 is a different type of update. The kind that even I actually did right away. It is a security update. One prompted by real world security issues.
This update adds no new features, but gives you protection. Apple recommends that users download the new iOS update right away.