Steam already uses highly efficient delta compression algorithms when downloading games. The download size is compressed significantly compared to the final size on your hard drive. How to Legitimately Compress TF2 on Your Hard Drive
While TF2 itself is safe to play on Steam, downloading "highly compressed" versions from third-party sites carries significant risks:
When you search for a "highly compressed PC game," third-party sites often promise a download size reduced down to 1 GB or 2 GB. How Data Compression Works
Highly compressed packages are usually static snapshots of old builds. Because TF2 is an online multiplayer game, an old client will not connect to official Valve matchmaking or modern community servers. Legitimate Ways to Compress and Optimize TF2
You can manually delete files that the game loads but are rarely used in actual gameplay.
Unnecessary files, such as older, rarely used maps, extra language files, or some cosmetic files, might be excluded.
While the idea of downloading a 500MB file that magically expands into a fully functional 20GB+ game sounds perfect, the reality of highly compressed modern PC games is often filled with malware, broken files, and broken promises.