Opinions on moonlighting? A negative connotation?

It really depends whether you are holding a full time job in the public or private sector. For public sector, moonlighting is prohibited. For private sector, moonlighting is fine as long as there is no conflict of interest between your full time job and moonlighting job.

As long as it doesn't affect your full-time job, i don't see any reason why it's a bad thing.

Public sector stricter on moonlighting, while for private, as long as you don't go signing another employment contract while still in your current one, or have a conflict of interest by taking on the side 'job' then I think it's fine. Conflict of interest can also mean...you find yourself spending more time doing the side 'job' and it's affecting your performance in your main job, then that's can issue.

Depends on your profession, most likely not an issue unless your employment contract specifically not allow u to do so. I know some ppl do part time property agent, the so called secret agent. The only sacrifices is you are trading your rest time with the part time job and eventually could affect your full time job performance.