I'm an undergraduate student applying to graduate schools. A few weeks ago I sent my application plans to the professors who will write me the reference letter. However, recently I decided to cancel some of my applications. In my reminder email, I just wrote to the professor "I cancelled my plans for XX university after consideration, but other applications are due...thanks for the help!" Is this okay? Do I need any further explanations? Thanks!
At least in fields I'm familiar with, it is very late to be cancelling letters, such that many might have started your letters. If you are able to offer a reason for while you are cancelling late that makes sense without making you uncomfortable to share, it might make people less upset with you.
That said, most people will probably respect your privacy and just be happy there's less work to do.
The major component of work for the recommender is generating the recommendation letter, not in going to each school's site to submit, so I don't believe your letter writers will have put major time into a school you opt not to apply to that they wouldn't have needed to do anyway.
What might be annoying is if I'm trying to submit a recommendation, and there's no place to do it when I log on to a site. That would start an email exchange that I didn't have to have.
I think notifying your recommenders that you've opted not to apply to every school you've told them about is fine, and can prevent confusion later.
For what it's worth, last week I had a student send me just such a letter, and it didn't annoy me at all (and I'm a pretty crotchety guy).