Like another question (to which Patricia Shanahan and I also provided conflicting answers), I will provide the perspective of US Pre-clearance in Canada. I can speak to Halifax, Canada (YHZ). Basically, there does not appear to be any reduction in the monitoring or checking for using Global Entry at YHZ.
Passengers using Global Entry didn't have to wait to use the normal Automated Passport Control terminals, and were called by the officers before any of the normal passengers. There is also a specific lineup for clearing the security portion which is handled by CATSA (the Canadian equivalent of TSA).
However as far as customs and immigration is concerned, I was still asked a couple quick questions, just like any other passenger. I'm a permanent resident, what was I doing in Canada (tourism), where was I headed (home), how did I get my permanent residence (employment). The rest of the questions would have been asked already by either the APC/GE terminal. I got a stamp and headed on.
Overall, at US Pre-Clearance at YHZ, Global Entry is mostly about getting access to a priority lineup.