I would keep it as a back up until you know ssd is working. Take it out of PC so you know windows can boot off SSD without drive being in case
Once it works, its your choice. You could keep as backup or you can wipe it and use it as storage. I can't decide for you but I always like having 2 drives in PC as then I can move all my library folders off C and a) Save space on SSD, and B) make recovering from a fresh install faster next time as all your documents etc are already on your 2nd drive and all you need do is redirect library locations.