I typically make smaller purchases more often.

Because of that, my protocol is to use self checkout until the amount/total size of items makes the tiny nooks too cramped for comfort.

I don't typically loathe human interaction enough to take huge measures to avoid it, but I do prefer avoiding when possible.

I can also see it if I was buying a combination/type of items that I don't wanna be judged for. I can't think of a realistic version of that (other than the meme'd stories of a cucumber and pack of condoms or supplies you could bury a body with, etc), but just the thought that someone might judge it is enough for certain people to avoid it.