We do not use canned responses just because they are common in support. Both the reasons you give there are true and both are important.
Consistency of replies is important. It keeps us from saying things we perhaps shouldn't. It also means we give better replies and nobody gets tired and types "done" or "ok" and closes the ticket. Those aren't really great replies. It also means that if I have to give you directions, I don't miss a step because I've given these directions six dozen times, and leave you wondering what you're supposed to be doing.
Our canned responses have all been proofread and checked to make sure they're complete. This has value! :)
Volume of tickets matters, too. We want to reply to everyone and make sure they get help. If we can give them a canned response and move on it means that they got a reply and we have more time to think about the really hard question someone asked that we have no idea how to respond to. Or that we can go do the investigation and take seriously the reports of poor player behavior, rather than either ignoring them or over-moderating things that aren't really a problem.
The biggest reason we use them is to save labor.
There's less than 30 volunteers responsible for running all of Homecoming, and only 20 of them are GMs or CRs who handle tickets and most in-game issues.
There's pushing 9,000 players on at peak times, and a group of 20 people spends their limited personal time making sure those 9,000 people are able to play and have fun. In general, we love to do it and are really glad to have the opportunity to help make Homecoming happen. But we only have so much time in the day to dedicate to things like video games. Every minute we spend writing a unique reply is one less minute someone didn't get help and couldn't play.
Yeah, we understand they can feel a little trite. We don't mean them any less than a message we hand-crafted, and in fact, we sometimes do better when we use the pre-written responses. Because of our limited staffing and to help keep responses professional and on-point, canned responses are a necessity.