Server authoritative movement causes many problems on multiplayer servers, like taking fall damage when you shouldn't, falling into lava when you shouldn't, combat is completely broken and sometimes you glitch into blocks randomly. Though this setting is on by default on worlds and realms and cant be turned off, on Bedrock Dedicated Servers, its optional, and in the change logs it says 'Server authoritative movement is still in-progress; we recommend not using it in this release.'
So WHY use it by default? This feature has ruined combat on worlds and has forced many players to stop pvping on worlds and moving to other servers or BDS, like me, and members of the factions and UHC community.