It’s also important to have logging plugins that work with CP. Stream is currently the most user-friendly one that’s compatible with CP.
There isn’t an email logging plugin that both works with CP and doesn’t have a broken feature, so I’m working on building that myself. (Actually, all working except for the fact that I haven’t decided how to handle attachments.)
REST API Log is important too for people, like me, who use the REST API a lot.