The main differences between split tunneling and full tunneling your traffic are speed and security. With a full tunnel, all traffic goes through your secure VPN connection, making it the more secure option; however, this can also lead to slower speeds due to the amount of traffic that needs to be encrypted and because when all traffic is sent via HQ, it overloads the HQ infrastructure.
With split tunneling, only part of your traffic is sent through a VPN, which means that things like video streaming and video calls will have better performance and there will be less strain on the HQ infrastructure.
NordLayer is currently working on a split tunneling solution and will offer complete functionality soon. For now, NordLayer only partially helps to resolve split tunneling use cases.