I do that sometimes. I sent an email recently to thank the author of XLD [0], an excellent piece of software hosted on Sourceforge, where I don’t have an account. I wouldn’t say it’s about low effort, so much as not taxing the recipient: with an email a person may feel more compelled to reply than with an opened and immediately closed issue.

[0] https://tmkk.undo.jp/xld/index_e.html