On general principles, and that you might learn something from them, but also because they grow up.
I got this email:
This is Small Dog, we met back in 2015 in Chicago when I was a grad student with OtherLovelyBigDog and you came to give one of our seminars. We also may have chatted briefly after your talk on the last day of Society Meeting last year?
Anyway, I’m writing because I was recently asked about presenting at a meeting on bunny hopping in NicePlaceinEurope. I won’t be able to attend but I recommended you as a speaker given your current work on bunnies. One of the board members for the meeting, Dr. European GrosseChien, has told me that the meeting organizers would be delighted to have you come and speak. Your expenses would be covered.
Small Dog, it seems, has landed a very luscious and prestigious postdoc with other BigDog. I remember him as being a very interesting student with whom I enjoyed talking very much.
And for the suspicious/paranoid amongst us, his field is sufficiently different from mine that I have (and will not) get his papers or grants to review. He's just being a Good Guy.