If you send a patch as an attachment to a Linux kernel list, or most of the mailing-list-based projects I contribute to, it will almost certainly be insta-NACKed: maintainers are basically too busy to deal with anything that doesn't exactly match what git-send-email generates.

From a maintainer POV this is honestly perfectly fair - we have tooling like Patchwork that depends on patches being submitted inline. From a first-time contributor POV, this just puts the barrier to entry up even higher. :(