I noticed with the new beta when i get my taxi instructions atc tells me the Radar Control frequency i am still learning a lot and am not sure when i need to contact Radar and what i need to contact them for

as if i dont change the frequency i still get handed off to the tower 

The clearance includes the Departure Frequency (Radar Control at some airports) so if you lose contact with Tower after takeoff, you can contact Departure.  It is not to be used on the ground.

Dave

Thanks