What are the consequences of only having a single molex connection to your GPU from your PSU instead of 2? I have a GTX 1080 and recently attached the second one as I realized it might be necessary. I did this practice with my 970 as well
You shouldn't be using any molex connectors to power the GPU you should be using PCI-e power connectors from the PSU. If the PSU lacks the proper connectors and you are using molex to pci-e adapters then you should be looking for a new/better PSU that has the proper connections for the card.