Help! Important question for those of you who have sat on graduate admissions committees and are familiar with the process!

Am I doing my undergrad students a disservice by encouraging them to use services such as Interfolio when possible? Is a letter of recommendation that is otherwise specific and detailed about the student’s strengths and weaknesses sabotaged because it begins “To whom it may concern”? Should the rationale for using Interfolio be addressed in the letter? Should it be avoided, or if the service is used at all, should I upload a separate letter personalized for each school?

I’m pretty sure med and law schools don’t really care, but what about graduate programs in the humanities?

I know many Graduate Schools of Arts and Sciences have shifted to electronic applications, which I personally find rather annoying and not much easier for me at all, but I don’t think all of them have.