How much do I need an "angle guide" for making a knife?

[yoyoma]

Still looking into options regarding doing everything with files vs getting a cheap 1x30 belt grinder, and I'm trying to figure out how much I need something to "hold an angle" when grinding the knife (before and after heat treatment).

Is it necessary or very useful? I'm worried about messing up the angles on the knife doing everything freehand, but am not sure if that's really going to be a problem.

Anybody with experience can answer?

Thanks!