In most cases, yes. But there are exceptions.
You can use the Add to List step in your workflow to automatically add people who text your keyword to a list (i.e. first-time guests, volunteers, etc.). This is helpful if you want to communicate with that group in the future. For example, you can use this step to easily for follow up with guests, communicate ongoing information about small groups, or share announcements with your church.
If you're using this step, you'll need to check "Opt-in subscriber to receive ongoing texts." under Additional Settings.
However, you may not want to use the Add to List step as part of your workflow if you don't want to contact that group in the future, like if you're using your keyword to get registrations for a one-time event.