The classic saying (and I use it often) is that "what gets measured, gets managed". If I know my manager will give me a raise if I acquire 100 clients, I'm going to know how many clients I have and when I get to 100.
Does this mean only things that matter have measurement? Nope. There are plenty of things that we don't measure that are critical.
It could be that they are hard to measure - there is no clear, easy way to get reliable data.
It could be that we don't trust the measurement - if we could measure it, would it be accurate?
It could be that it isn't worth the effort - I could measure it and it would be accurate, but it would take too much time and effort.
Each business will be different. A business that focuses on sales would need more sales metrics. One focused on quality would want more quality metrics.
The manager needs to know what they want to measure and determine if it is possible and worth it. My experience has been that most measurements are possible, but often times they aren't worth it because of the effort or the reliability. Yet, if it is important, it makes sense to start measuring something and then learn how to make it better.