It depends. Sometimes, yes, users do have many different conversations going & tabs for different conversations.

Or they might be flipping between different sheets in the spreadsheet. And perhaps those sheets have cross relationships. Or perhaps the user changes which sheet they're looking at & has old data.

Whether or not it's common doesn't change that it's a concern that good developers strive to develop for, and it's something that ought be expected. Tabs are part of the web, are something that support user-agency, and it ought to be common that they are well supported. Now, we can start doing the job we ought to do.