The M1 garand is semi-automatic for one, which means that you don't just spray and hope you'd hit the head of the zombie since as you should know, a headshot is the only real way to kill a zombie and with an automatic weapon you'd be wasting every round of ammunition that isn't a headshot and if you spray and pray you're very unlikely to get a headshot.
The M1 Garand is a very durable weapon that was used by the US army for a very long time.
With the M1 Garand you'd pick your shots wisely since you know you've only got 8 per clip.
Also, you can stick a bayonet onto an M1 Garand
But, the M1 Garand also sucks against even zombies in WaW(which was a failure of a game) and is only worth using in hardcore possibly as a semi-automatic sniper rifle, as said above by dutchmandan.
It's also much lighter and easier to carry than a bolt-action rifle or an automatic rifle with all that ammo you'll need to use it.
If you're too lazy to read all of that I'll sum it up in one sentence, the M1 Garand is amazing.