A:

A "linked" node is depicted by the purple outline and the        icon. It gives buffs, such as seen here: 

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A "local" node is depicted by the orange outline and often the         icon. It also gives buffs, such as those seen here:

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The primary difference between the two is that linked nodes buff additional nodes, whereas local nodes maintain their own buffs. Once that link is gone, the additional buffs from linked nodes are removed, and, if it is a local node, the local nodes buffs remain.