ShaderLab - What is "RenderType" subshader tag used for?

I'm slowly trying to get more familiar with coding and reading shaders. However, I'm running across a subshader tag that I'm not finding any reference on in the Unity ShaderLab Reference

The subshader tag is the "RenderType" tag. For example I've seen things like "Transparent" and "TransparentCutout". However, I'm not understanding what this tag is used for. Could someone tell me what it is used for or be able to point me to a forum or answers link (I wasn't able to find one)?

Thanks!

As far as i know it's only important if you want to use replacement shaders.