Unity Architecture

Mono vs IL2CPP

Mono (Old)	IL2CPP (New)
Uses Just-In-Time (JIT) compilation	Uses Ahead-Of-Time (AOT) compilation
compiles code on demand at runtime	compiles entire application before it runs

IL2CPP is better at floating point math than Mono.

The benefit of using a JIT-based scripting backend is that the compilation time is typically much faster than AOT.