collect is used to send data to Google Analytics about the visitor's device and behaviour. Tracks the visitor across devices and marketing channels.

GPS is used by youtube.com to registers a unique ID on mobile devices to enable tracking based on geographical GPS location.

VISITOR_INFO1_LIVE is used by youtube.com to Tries to estimate the users' bandwidth on pages with integrated YouTube videos.

YSC is used by youtube.com to registers a unique ID to keep statistics of what videos from YouTube the user has seen.

r/collect is used by doubleclick.net for session management.