Nginx proxy websocket: is it required to close the connection to backend after upgrading to a websocket?

Base on what I could read on nginx site https://www.nginx.com/blog/websocket-nginx/

The exemple they give will close all connections to backend. This isn't really what we want on a proxy setup, forcing to reopen a connection to backend on each new client.

http {
    map $http_upgrade $connection_upgrade {
        default upgrade;
        '' close;
    }
 
    upstream websocket {
        server 192.168.100.10:8010;
    }
 
    server {
        listen 8020;
        location / {
            proxy_pass http://websocket;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection $connection_upgrade;
            proxy_set_header Host $host;
        }
    }
}

But is it required to close the connection after upgrading to a websocket?

can't we change the map so it maintains the 'keepalive' connection to the backend ? (for all non websocket requests)

    map $http_upgrade $connection_upgrade {
        default upgrade;
#       ''      close;
        ''      '';
    }

Being the only user on a test environment it didn't seem to create any issues, but will it be the same in production?