SMBIOS is a structured table that the BIOS/UEFI builds when the computer starts and leaves in memory for any program to read. It describes the motherboard, CPU, RAM, chassis and more.
Why anti-cheats value it
What makes SMBIOS a strong fingerprint is that it is filled in before Windows even loads. It holds, among other things, the system UUID and serial, the motherboard serial and the chassis tag. Because it is established by firmware, ordinary software cannot simply rewrite it.
What this means for an HWID change
This is the honest part. A software HWID tool — HWIDChanger included — changes the identifiers that can be changed safely from Windows: the Windows IDs, the disk volume serial, network adapter (MAC) addresses. It does not change SMBIOS, because SMBIOS is firmware-resident. Tools that claim to rewrite the SMBIOS UUID operate at firmware level (a BIOS reflash or a low-level driver), which is risky and can leave a machine unbootable.
So how far does a software change get you?
For most software DRM and many game anti-cheats, changing the Windows, disk and network identifiers is enough to look like a different machine. Against the strictest kernel anti-cheats that specifically read SMBIOS — Vanguard-class systems — a software change has a real limit, and the only sure way past it is different physical hardware. Knowing that up front is better than expecting a tool to do something no safe software can.