No, not every user needs a Q&A role. Only users who will participate in the Q&A process need a Q&A role.
You can set up a buyer group and decide to only grant access to the Q&A tool for a selection of users in that group.
Note: Keep in mind that users without a Q&A role cannot see any questions or answers asked in the Q&A tool. This makes it impossible for them to participate or collaborate.
You can make a distinction between Question Drafters and Question Submitters, or when you want to exclude users, no Q&A role. See the example screen below:
Q&A Tip: If you want to change one of your user's Q&A role, visit Change user's role to learn how to perform this action.