I currently have an HTC 10 -- Soon maybe Galaxy S8 (dreading it though -- but I need to keep hopping phones due to JUMP on Demand). The thing is that HTC's stock ROM has so little bloat that can't be removed, that there really isn't any need to remove it to gain performance -- however if you want granular control over the phone software, rooting it is quite nice. Having Xposed/Root. HTC themselves have stated specifically that hardware warranty will not be voided even if you have unlocked bootloader/rooted.
If you want to make root and still take OTA (I don't know if the M8 can still get OTA updates or not), look into Magisk, it'll also pass SafetyNet -- allowing you to use Android Pay.