Is line progression a thing or not?

How come some people on here test every day to see their line progression, and others say that the darkness of the line doesn’t mean anything? I would have thought that the more hcg you have (ie the more pregnant you are) the darker the line would be and therefore line progression is important? Also, I’ve had a chemical before and my lines got lighter, that’s how I knew something was wrong. So surely you want to see them get darker? Help a confused very early pregnant lady out please! 😆