Does Series 8 "always" mean it can be set to be always on but can be used without always on?

No, it doesn't have to always be on. You can turn that feature off or on as you wish. See the following from Use the Always On feature with your Apple Watch - Apple Support

How to turn the Always On feature on or off

1. Press the Digital Crown until the Home Screen appears, then tap the Settings app .
2. Tap Display & Brightness.
3. Scroll down, then tap Always On.
4. Tap Always On to turn on or turn off the feature.

No, the "Always On" feature allows the user to choose how to turn the feature on or off. Use the Always On feature with your Apple Watch explains...

"How to turn the Always On feature on or off

1. Press the Digital Crown until the Home Screen appears, then tap the Settings app .
2. Tap Display & Brightness.
3. Scroll down, then tap Always On.
4. Tap Always On to turn on or turn off the feature.

Always On isn't available when your Apple Watch is in Low Power Mode or Theater Mode, which you can turn on or off in Control Center."

You are welcome.