Does factory reset clear system data on Mac?

I have done this on 3 Macs. Boot into recovery, erase the drive, reinstall the OS then migrate your files and the other system data will drop considerably. However, over time it may start to grow again. My last Mac went for 110GB to 70GB of other system data. The drive needs to be erased not just reinstall the OS.

OP wrote " I read somewhere on this forum that factory reset didn't help them but that was only 1 case that I found. "

Most probably that user may have used Setup Asset and Migrated ALL their previous data, applications etc back into the Pristine and Virginal re-installation

Issues that may have existed when the TM Backup was made would have been migrated to the New Installation

A Factory Reset ?

There are two very distinct Factory Resets

Both will remove the " system data "

One is for Intel Computers and will involve Reinstalling the Operating System

For Apple Intel computers, use Disk Utility to erase an Intel-based Mac and then follow the instructions in How to reinstall macOS.

The Other for Apple Silicon M-Class computers will also remove the " System Data "

It Will Not Touch the existing and installed Operating System

For Apple Silicon computers, use Disk Utility to erase a Mac with Apple silicon

MacDataSaviour wrote:

Yes, a factory reset will erase everything on your Mac, including system data, and restore it to its original state.

Not entirely correct if the computer is Mac with Apple silicon or the Apple T2 Security Chip

Erase your Mac and reset it to factory settings

Use the Erase All Content and Settings feature to quickly and securely erase all settings, data, and apps, while maintaining the operating system currently installed.

You’d have to explain what you mean by a “factory reset“System data is not data used by the system, it is data that cannot be categorized by Spotlight into one of the other bins. It is not data that is stored even with the system. So, Erase all content in settings would achieve what I imagine you want.

local Time Machine snapshots is part of what is system data, and I also think it is any SSD storage areas that have not been reset into write mode after deleting data.

Yes, a factory reset will erase everything on your Mac, including system data, and restore it to its original state. However, if the system data is extensive, it could be due to cached files, logs, or Time Machine snapshots. Before resetting, try reducing system data by deleting local snapshots (tmutil listlocalsnapshots / in Terminal) or clearing caches. If that doesn’t work, a factory reset should clear all system data, but ensure you back up important files first.