Apple Watch - Erase All Content and Settings

You're welcome!

They are the same, except that, when unpairing via the Watch app (which is the recommended process):

• A fresh backup is made of your Apple Watch on your iPhone before your Apple Watch is erased, which then removes all contents and settings.
• Activation Lock is also removed from your Apple Watch, which would leave it ready for a new user to set up as their own.

More information:

About Activation Lock on your Apple Watch - Apple Support

Hi

Historic Health and Activity data is stored on your paired iPhone, not on your Apple Watch.

If you erase your Apple Watch (such as by unpairing it via the Watch app, which includes syncing the latest Activity data and making a fresh backup of your Apple Watch on your iPhone) and then re-pair it, your historic data on your iPhone will not be affected.

If you plan to erase your iPhone, then, in order to retain your historic Health and Activity data, make an encrypted backup of your iPhone first and then restore it from that backup afterwards.

More information:

Unpair your Apple Watch and iPhone - Apple Support

Set up your Apple Watch - Apple Support