Security updating is an awkward thing. Microsoft knows from experience that people will delay or ignore essential patches, leaving their systems exposed to exploitable flaws. In response, Windows 10 is proactive in installing critical fixes and in rebooting to ensure that those fixes are actually active. This is good for patch adoption, but it's bad when a reboot comes in the middle of a presentation or an online game or anything else that you don't want interrupted.
With the Windows 10 Creators Update, Microsoft is hoping to ease some of this pain. When an update has been downloaded, an alert will show three options: install and reboot immediately, schedule a time (within the next three days) to install it, or snooze the alert to temporarily delay the decision. This won't let you delay an update indefinitely, but it should offer a reasonable trade-off between the need to get systems updated and the annoyance of interruptions.
The large Windows updates (such as last year's Anniversary Update and the imminent Creators Update) bring frustrations beyond the automatic rebooting. Their rollout is handled very conservatively, with Microsoft pushing out the software first to known working configurations (such as systems that were extensively tested by OEMs or Insiders) before deploying it more widely. Similarly, the update will actually be held back from systems with known incompatibilities. This situation leads to some confusion and frustration, especially among enthusiasts: one PC may update immediately, while another takes much longer to receive the update, with no obvious rhyme or reason for the discrepancy.
from Windows updates to become more reliable and predictable, with fewer surprise reboots