Then the manager will usually schedule an exit interview for the report (or, if you’re at a bad company, fire you on the spot).
On the other hand, I don't react well to having news spring on me. My heart can race, I need some time to think through it by myself in order to be ready to discuss it rationally. I doubt I'm the only IT person in this boat. And likewise, if I'm delivering bad news, I end up spending more time worried about reactions that properly explaining myself. So a note in advance, to break the tension, could lead to a more effective conversation, vs. surprising someone. I understand there could be legal reasons why you'd have to terminate someone in person, but outside of that, it's nice to give people time to consider what they'd like to discuss before pulling them into a discussion.
The first meeting I don't beat around the bush, I get to the point within 60 seconds. I explain what I need to explain, and don't really leave them a chance to feel like they need to talk.
I finish up by telling them if they have any questions right now I'm totally happy to answer them and discuss, but I'm scheduling a follow-up meeting at $earlyTime tomorrow so they can sleep on it and we'll check in and have a follow-up conversation. And also that if anything comes to mind late tonight, they wake up in a cold sweat, whatever, to give me a call and I'm happy to talk whenever.
Because yes, even the most composed people I've worked with have been thrown for a loop by stuff like this and the first meeting is never really a productive two-way conversation. I just try and make it make as much sense as possible and don't take anything personally, and then have the real conversation about it the next day.
Funnily enough my boss had the same idea so we were both informing each other that we were leaving, in the same conversation.