@Joshua Rogers: No. Apple has been applying far too much thermal paste to its systems as a matter of routine for many years-going back to at least 2008. So much, in fact, that people sometimes see a temperature decrease of about 5*C by reapplying the thermal paste on the Macbooks and Macbook pros correctly. Compared to the mess they make in the laptops, those GPUs are actually pretty clean.
The IR sensor cable also connects the Hall Effect switch that detects whether the lid is closed or open (and thus shuts off the display, puts the computer to sleep, wakes it up, etc.) to the logic board.
How do I know? I re-pasted my late 2011 17" MBP and forgot to reconnect it. The machine would not sleep automatically when the lid was closed anymore. Re-connecting the cable fixed it.