[Jotaku]

In many games, Immobilizing means just "being unable to move" which means it allows attacking or using skills. However, immobilizing means differently in Eternal Return. 

In Eternal Return, immobilizing is triggered by any kinds of CCs that makes enemy being unable to move either short or long time. For example, root, stun, knockback, knockdown are all considered to make immobilizing effect, while all of them except root also make the target unable to attack or use skill.

Thay's why so many people use Thorn Shackcle in suppot augment.

Plus, traps trigger augments also, so double guillotines can proc thorns and diamond shard.