I feel I need to weigh in here, as I'm probably seen as one of the main "offenders" in this regard.
The objection to the use of canned greetings seems to be that it's annoying to long-time users. Well, sorry: you all aren't who these comments are for. These comments are for the new users who have stumbled into our midst, generally with good will, but with very little idea of how we expect them to behave, and as such they often behave in ways we feel are inappropriate. That said, new users are the lifeblood of this (and other) stacks; if we can't encourage and keep new users, then we'll wither away. These new users also haven't seen the same greeting again and again, so they aren't yet as jaded as some of present company.
The other side of the coin is that, like others, I've put a lot of time into reviewing new users' posts on SE Home Improvement. It's important work, not only to be friendly to new users but to redirect and (if necessary) flag bad actors. It's also important that it be efficient. To date I've reviewed close to 24 thousand posts. Let's say I write custom messages and spend thirty seconds on each, that would take over a month at 40 hours/week. Sorry: no can do.
So, I use AutoReviewComments, and tweak the wording so as to be welcoming and helpful. New users' reactions have generally been quite positive; they are grateful to be told they're welcome, that they're doing fine (or how they're not), and where the Customer Service counter is.
So, these comments are clearly useful and generally welcomed by new users. For older users who get annoyed by them, all I can say is that I'm sorry you're find them so cloying, but I'm confused as to why you care enough to complain. And, if you feel you can do better, then please dive on in and review some posts.
P.S. Here's my AutoReviewComments configuration for DIY:
###[A] Adding question as an answer
If you'll take a couple of minutes to [take the tour](//$SITEURL$/tour) and read the help center, you'll note that this is a Question & Answer board, not your run-of-the-internet discussion forum. As it stands, you've asked a **Question** by posting it in the box marked **Answer**. Now there's nowhere for someone to answer your question. Please feel free to [ask a whole new question](//$SITEURL$/questions/ask) - nobody will think poorly of you for doing so.
###[Q] XXXX, please take tour
[type here] And, you should probably [take our tour](//$SITEURL$/tour) so you'll know you'll know the details of contributing here.
###[Q] Shopping Question
Unfortunately, "shopping" questions are off-topic here. Please [take our tour](//$SITEURL$/tour) so you'll know how best to participate here.
###[Q] Opinion-based
Unfortunately, any answer to this question will be a matter of opinion. Please [take our tour](//$SITEURL$/tour) so you'll know how best to participate here.
###[Q] Accept your answer; take tour
If an answer is helpful, please click the large check mark next to it to accept. And, please [take our tour](//$SITEURL$/tour) so you'll know the details of contributing here.
###[Q] Need more info
Unfortunately, we'll need more info before we have any chance of helping you. Please [take our tour](//$SITEURL$/tour) so you'll know how best to participate here.
###[Q] More than one question asked
It is preferred if you can post separate questions instead of combining your questions into one. That way, it helps the people answering your question and also others hunting for at least one of your questions. Thanks!
###[A] XXXX, take our tour
[type here] And, you should probably [take our tour](//$SITEURL$/tour) so you'll know how best to contribute here.
###[A] Good answer
Thanks for the answer; keep 'em coming. And, you should probably [take our tour](//$SITEURL$/tour) so you'll know the details of contributing here.
###[A] Answers just to say Thanks!
Please don't add "thanks" as answers. Invest some time in the site and you will gain sufficient [privileges](//$SITEURL$/privileges) to upvote answers you like, which is the $SITENAME$ way of saying thank you. And, you should probably [take our tour](//$SITEURL$/tour) so you'll know how best to contribute here.
###[A] Nothing but a URL (and isn't spam)
Whilst this may theoretically answer the question, [it would be preferable](//meta.stackoverflow.com/q/8259) to include the essential parts of the answer here, and provide the link for reference.
###[A] Requests to OP for further information
This is really a comment, not an answer. With a bit more rep, [you will be able to post comments](//$SITEURL$/privileges/comment); in the meantime, please [take our tour](//$SITEURL$/tour) so you'll know how best to contribute here.
###[A] Interesting, but doesn't answer the question
This is interesting, but doesn't answer the original question. Please [take our tour](//$SITEURL$/tour) so you'll know how best to contribute here.
###[Q] OP now has two accounts
It looks like you now have two separate accounts; you should [request that they be merged](//$SITEURL$/help/merging-accounts). And, please [take our tour](//$SITEURL$/tour) so you'll know how best to contribute here.
###[A] OP now has two accounts
It looks like you now have two separate accounts; you should [request that they be merged](//$SITEURL$/help/merging-accounts). And, please [take our tour](//$SITEURL$/tour) so you'll know how best to contribute here.