The witness role is to run the blockchain here. The top 20 witnesses get paid 7000 Steem per month for their role. These 20 witnesses also validate the most blocks that are produced. The other witnesses get less blocks but still validate some, the number I don’t know.
When we do a fork like we just did the majority of the witnesses need to also update their version to ensure continuity. If 15 witnesses update their node but 5 don’t then that creates a problem and a separate chain gets created. I don’t know if you’ve seen the ethereum split; there is now Ethereum and Ethereum classic. This is because they tried to fork but a bunch of people said no so it divides the chain.
The new witnesses get to add their node to the chain to ensure continuity but also learn more about the programming. What I’ve heard is the scripting here is not intuitive at all and difficult for developers to get used to. I don’t script so I can’t say if that’s true or not but the more people that add a witness node the better. The top 20 witnesses have mostly been there for so long that lots of the users who voted for them have probably quit so they aren’t necessarily the best to run it, they are just staying there by default almost. This is why I’ve removed my vote for the top 30 witnesses and voted for those I know or are in the bottom 70-100. The new witnesses are who are going to improve this place in my opinion, not necessarily the current top 20.