Because Siri knows locations (iPhone 4S or later) like “current,” “home,” and “work,” it can remind you to do a certain task when you leave a location or arrive at a location. Tell Siri “Remind me to call my daughter when I leave the office,” and Siri does just that.
Location information isn’t tracked or stored outside iPhone. You can still use Siri if you turn Location Services off, but Siri won’t do anything that requires location information.
Turn off Location Services for Siri: Go to Settings > Privacy > Location Services.