###Canned responses
I don't speak for others. I do however consider it useful to have stock comments. I call them canned responses, which I often tailor to specific users. I check out user profiles to see if the user already knows the SE culture in general even though they're new to the site.
It should be noted that slapping a one-size-fits-all comment on everything isn't always helpful. Sometimes it does cause confusion. So I recommend having canned responses, but also modifying it to fit the situation as far as possible.
Auto Review Comments is a useful Chrome extension to help with this.
###Welcoming new users
Although it's not mandatory, I think it's only natural to preface our comments with "welcome to [sitename]" when we see new users. I have been doing so for 4 years on any site I frequent (especially ELU). Considering that this is IPS, it makes even more sense to be friendly to new users.
But here's the thing though. I don't necessarily suggest being okay with poor quality posts or turning a blind eye to bad things happening just because some user is new. With zero hesitation I'd empty my flags, votes or thunderbolts, and I'm lavish like that.