If you download a pirated version, you lose access to the millions of free community-made maps, models, and game modes (like Prop Hunt or Trouble in Terrorist Town) that make the game fun.
If you are looking to get your hands on (GMod), it is important to know that it is a paid commercial product. While you might see links promising a "free download," these are often unsafe or unreliable. Where to Safely Get Garry's Mod Garry’s Mod Free Download
Downloading from official sources ensures you aren't installing malware, miners, or viruses that are common in "cracked" versions. Why the "Free" Versions Often Fail If you download a pirated version, you lose