Yes, it is safe. It won't cause a big loss on your iPhone. What you will lose is the Home data, Health data, iCloud Keychain, Payment information, Siri, Wi-Fi network, etc. Additionally, resetting end-to-end encrypted data will reset many other settings on your device. Such settings include Apple card transactions, Health data, Home data, Keychain, Maps Favorites/Collections/Search history, Memoji, Messages in iCloud, Payment information, QuickType Keyboard, learned vocabulary, Safari History, Tab Groups, iCloud Tabs, Screen Time, Siri information, W1 and H1 Bluetooth keys.