1. Might be good for improving your mood. Personally, I think it would improve your mood by stimulating your brain cells to grow & be active. On the other hand, some people suspect that a language designed to be cute, good and happy might make you cute, good and happy.
2. You have a chance of finishing. The language uses lots of tricks to keep the vocabulary burden down. Likewise, grammar is restricted to a few regular and predictable constructs. Learning a natural language, or even Esperanto will require a much more significant investment of time. Toki pona is about a month of work to read and write at a basic level.
3.You probably will be able to pronounce it. The sounds in toki pona also exist in most other languages. There are fewer sounds, so even if you consistently use the wrong consonant or vowel, you probably will still be understood.
4. Toki Pona is the hottest constructed language since Klingon. See reasons 2 & 3 if you think Klingon might be better. And if you think French, Spanish or Tamil are hotter languages, also review #2 and #3 again.
5. (For English Speakers) People would rather speak English to you when you travel anyhow. At least in West Europe. I keep trying to use my broken French, Spanish, Russian when I have the chance and mostly people would rather hear me speak English. I can hardly blame them, I’m often unintelligible in English, let alone Russian. In toki pona, everyone is a bit hard to follow, so I’m on even footing.
6. It makes an excellent code language. Natural languages are some of the hardest codes to crack. Toki pona with its words that change depending on context gives you plausible deniability, i.e. maybe you are speaking in code, maybe you are meaning what you words say on the surface. [*sadly, I'm not expert enough to generate a good example, that would take more than a month]
7. You’ll be able to say you are bilingual. It’s a good resume filler.
8. You could teach it to your children and they would be bilingual. It will either make them smarter and if not that, then it will be a good resume filler for them.
9. It is probably machine parse-able. Handy if you are a computer scientist.
10. It’s (possibly) a window into the early days of human language. In the beginning there was a word. Or two. Or at least so I imagine. Somehow, people made themselves understood with a smaller vocabulary.
11. It’s good for brainstorming. Translation into toki pona or even writing toki pona requires constantly thinking of alternative way to express things.
12. It’s a drug free way to see the world in a different light. Reading toki pona induces a sense of creativity, since the constant ambiguity forces you to consider bizarre, whimsical or potentially profound new connections between seemingly unrelated things.
I don’t think any language is a good auxiliary language except the most widespread spoken language of the moment. It’s not economically rational to pick any other language to be the auxiliary language.