Spine and leaf architecture - connections to leaf switches
In a network employing spine and leaf architecture, all servers and other network devices should be connected to leaf switches. Also, any uplinks to other parts of the datacenter or to more traditional networks should also take place via a special leaf switch called a border leaf.
You can read more about how you should connect spine switches in this note:
Spine and leaf architecture - connections to spine switches
One of the reasons why we connect leaf switches in a certain way is to reduce latency: