[Clfs-support] Why cross-compiling?

[booleandomain]

Hello,

I'm a CLFS newbie. I don't understand why cross-compiling tools such as 
binutils and gcc. Let me explain. My CPU is an Intel Core 2 Duo. The 
host system is Gentoo Linux running on that CPU. uname -m returns 
x86_64. I want my target Linux system to run on the same computer as the 
host system, so the target should return x86_64 too. So why putting 
x86_64-cross-linux-gnu for --build and --host and x86_64-pc-linux-gnu 
for --target? It should be build=host=target=x86_64-pc-linux-gnu (native 
mode).

Thanks.