WiFi Tether without paying extra to the carrier for the same data you're already paying for is a feature.
Backup specific apps and their data ("Titanium Backup" or its successors) or the entire device ("NANDROID" backup via TWRP, CWM, PhilZ, etc)
Root apps allow flexibility carrier-ROMs don't. Greenify shuts down unused apps. Xposed allows changing almost anything about Android operation (the "framework") with easy installation. See this link for top rooted apps.
None of these are available with locked bootloaders, and stock ROMs. (The NANDROID backup is available with stock ROMs but is if little value).
MotoG4 using Silesh Nair xt16xx 7.1.1 Lineage OS 20170113 ROM