I use indirect buffers when I want to narrow to different parts of a long file. (I usually use outline-minor-mode not actual narrowing for that.)

I don't use indirect buffers often and am not familiar with the inner workings, so maybe I make some incorrect assumptions here:

Explicitly turning diff-hl-mode off might be a good idea; I think indirect buffers otherwise end up with stale diff-hl information. Even better though would be if the diff-hl information in indirect buffer did get updated, but that would have to happen after the file-visiting buffer has already been reverted (and therefor the indirect buffer too).