One by one, US ports of entry are introducing "automated passport control" for holders of US and Canadian passports. More details and lots of opinions in
this FT thread.
In a nutshell, more and more people (US and Canadian citizens plus people who've paid for Global Entry and related programmes) are getting to go through the first stages of entering the country without being questioned by a human. They scan their passports, answer questions via a screen and get 'receipts' from the machines. They then need to hand over the receipts and show their passports when exiting the customs area -- at which point they may be asked one or more questions.
A side effect is that permanent residents now have to queue with visitors.
US LPRs had to line up with visitors at some US ports of entry even before APC kiosks were acquired for use by any US airport/airline; and in some places the US LPRs being relegated to the visitor lines took place even before there were GE kiosks. Just want to make sure that APC kiosks aren't seen as the driver of all of the shifting of US LPRs into the visitors' lines; that is not to say it may not have been a contributing factor at some airports and won't become more of one unless and until (or even after) APC kiosks are enabled for LPR use and perhaps even ESTA/VWP visitors.