I have a few open source packages.

Pros:

• You learn a lot. Like really a lot. About common bugs, build system and language specific stuff.
• People think you are omniscient because you are the maintainer
• You learn a lot about remote debugging and finding potential bugs with minimal information people provide
• You learn how to properly ship software, versioning, changelogs and also test. I once published a fix which was broken and soon after I got like 20 issues about the new update is not working. You'll shit bricks if you know that thausands of people relying on you to properly ship working version
• You mostly will learn how to test software
• You get a lot of traction (got a few job interview invitations because of my github profile)
• You learn how to make decisions in terms of the scope of your software and the features. You need to see the whole picture, while your users only see their use case.

Cons:

• People are sometimes, bitchy and demanding and also rude.
• In certain stages it is a ton of work, which does not involve coding like writing documentation, and support.
• Support. Most of the issues created in my repos are support stuff or questions.
• You will mostly not make any money out of it. Yes there are opencollective and patreon or donations. However my feeling is that even the really big repos get only peanuts out of it. I also tried a donation concept, however it is not working.