Kelpierion

The chassis to me seems to haunt the narrative of Portal 2 as a representation of corruption/ loss of self in the name of progress at any cost, reflecting Aperture Science's demise as a whole. How putting someone in it both times lead to chaos of the facility. Throughout the game it's been treated in a body horror light: The transfer, Caroline's backstory, and how it affected Wheatley.

With Caroline it represents her loss of autonomy and loss of humanity that made her into the GLaDOS we know. The process of being stuck imported into a machine with processes so advanced it'd break a human mind is such a terrifying concept. It's questionable how much of Caroline's identity was left in GLaDOS given she likely had an ego death; She's still implanted in there, but GLaDOS replaced her while still being her. Removing her from the chassis made her recall by being able to think separately from the facilities influence as herself.