r_3dnow “0”

What is this and why is it in mah hl2dm?
I figured my old PC was shitty and outdated and thats why 3d now would always auto-disable, but now it does it on my new one as well.

Is it even useful?

My apologies if this has already been covered in another thread, for I am far too lazy to go and look.

Did you try google? 3dnow is a graphics focused extension to x86 built into mostly just AMD CPUs. It was a big deal back in the day of AMDs climb to prominance, part of why AMD cpus were better for gaming then. People talked more about SSE after that.