Most gadgets benefit from periodic reboots, but the Apple Watch is different. According to Engadget, watchOS is lightweight by design and keeps its own house in order, so you don't need to schedule restarts. The operating system suspends apps quickly and manages caches without user intervention.
Restarting can still help when you encounter bugs, freezes, or unexpected slowdowns. If the watch becomes totally unresponsive, you can force a reboot by holding the side button and Digital Crown until the Apple logo appears. Apple also recommends restarting if there isn't enough room for an update, and you can manually clear website data in Settings.
Engadget's hands-on testing found that some Apple Watches went years without manual restarts and showed no serious performance issues. The reboots that happen automatically during watchOS updates are usually enough. For maintenance, focus on app and OS updates and keeping storage usage under control rather than preventative reboots.