Arista EOS: trunk group

From the below link of "MLAG - basic configuration", there have the following configuration of MLAG peer link VLAN:

vlan 4094
  trunk group peerLink
interface port-ch 2000 
  switch trunk group peerLink

Why do we need to assign vlan 4094 to trunk group? Quota from the reference of EOS configuration - VLAN,  

"VLANs configured in a trunk group are 'pruned' off all ports that are not associated with the trunk group". 

• So if you have other ethernet or port-channels are configured as trunk, by default ALL VLANs are enabled if you don't specify the VLAN range. In this case, peerLink VLAN is also included. This is not an expected behavior or good practice, since the peerLink carries the critical control plane information. 
• But if you configure VLAN in trunk group, you have to specify the physical interfaces are associated with this trunk group. This is to provide a casual configuration causing the disruption of peerLink Vlan