Tags help to understand complex categorisation which is not usually possible with “linear” categories.

A ticket with Email and LAN tags is surely different from a ticket with Email and Exchange tag. Both incidents refer to problems with Email but in one case it is most likely related to LAN issues and the other with Exchange.

You can use as many Tags on a ticket as required.

Tags defined here have no impact on reports unless tickets are assigned tags during creation or you have predefined Tags in service items.

Refer section on Dashboard and Reports to understand impact of using Tags.