Just wanted to share my recent experience in Terminal 1 from a couple days ago.
First time being in this terminal. All of my experience with Pearson is from terminal 3 for all my recent domestic travelling.
Terminal 1 seemed smaller. Which seems strange because it handles all the international flights. It was very busy, but I was still able to easily walk back and forth between E71 and E79. Then at 8pm all hell seemed to break loose. A whole bunch of flights started boarding, and suddenly it became impossible to navigate the E70 portion of the terminal.
Qeues to gates started spilling out across the terminal and qeues next to each other started mixing into other qeues. The terminal suddenly became crowded.
Traveller's were clearly confused, not sure which line they were supposed to be in, stumbling around with luggage and screaming children, bumping into other people.
I watched as 3 seperate qeues for Paris, Amsterdam and Istanbul essentially turned into a giant mass of people, and the airport staff were frantically trying to sort everyone out. Economy fliers lining up in the business class line, people with strollers missing the earlier request to board, etc.
Thankfully my flight wasn't until 11:35pm, so I got to watch all the madness ensue. My flight was out of gate E72. There is no room for qeueing in this part of the terminal.