Most experts recommend a value between 2 and 5 . Setting this too high (e.g., 20) can lead to server bans, connection resets, or CPU bottlenecks.
If a server is very slow, downloading more files at once is better than splitting one. Advanced: Domain Rules jdownloader 2 multiple connections
If you want to use different connection settings for specific websites (e.g., 20 connections for Google Drive but only 1 for a specific file hoster), you can use the feature: Most experts recommend a value between 2 and 5