Each website is different not only by design, but also by the amount of people that are using it. This not only affects the decisions made by the developer team, but can also influence the user experience.
Influence on user experience
You can compare a busy website to a busy online game. For example, when a lot of people are connected to play CSGO or LOL, you see a slowdown from the server side as it cannot give high quality and fast services to everybody at the same time.
The same is with betting or other websites that have multiple people in it at the same time. You can see an example here. When there are a lot of people connected at the same time and they are making decisions on who is going to win, it might influence other bettors.
Let’s take an example: 2017 China regional CSGO finals. There were 95 votes for TyLoo and 172 EHOME. When a new visitor comes online, it might influence his or her voice: if a lot of people are rooting for EHOME, maybe they should too?
Influence on servers
We have all been there: you are playing or betting and the website crashes because there were too many requests. Keeping an eye on the usage statistics, you can see when you should visit the website: maybe there are hours when there are less than usual visitors?
The amount of website visitors is important not only to the developers, but also to users. By knowing the load, you can better plan your visit time.