When should I associcate the site collection created by teams to hub?

Hello tom_s1865 

when you use the SharePoint Site in a HUB, as example in a Project HUB, when you have a Teams per Project and with a Hub you inherited the design, navigation and search scope. See more: https://learn.microsoft.com/en-en/sharepoint/planning-hub-sites

P.s.: HUB Sites are an M365 feature only, nothing to do with your labels like SharePoint Server.

Regards, Dave