Potentially Quick to Learn
It has 125 base words, but still is expressive enough to discuss many topics. From my experience, an 8000 word Russian dictionary is too small to get through a month’s worth of conversations of daily life.
There are many applications to quick to learn languages, for example, in a refuge camp with speakers of a dozen languages, it might be easier to teach everyone Toki Pona than to teach them all English or wait for a pidgin to form naturally.
Warning, word for word translation is not enough for full understanding. Just knowing the base vocabulary only gets you part way to fluency. Many compound words are idiomatic, for example, here is a machine word for word translation of Stairway to Heaven. Here it is in the toki pona.
Potentially Easy to Pronounce for many
Even if you can’t get one or two of the consonant or vowels correct, say if you pronounce l and r the same, you will still be intelligible because there isn’t an r is the toki pona alphabet.
Early Language Acquisition
Some parents are teaching their children sign language, because kids can sign faster than they can physically speak the words. Presumably, if the audible language was simpler, they’d pick up the language even faster. On the other hand, learning two languages in parallel might slow language acquisition because you hear fewer examples of each in the same time period, or maybe it speeds language acquisition because the brain gets more linguistic stimulus.
If nothing else, the idea of teaching constructed languages or sign languages to children sure does get some people riled up, since they figure if you are teaching your child a language other than English you must not be speaking English at all.
Test Hypothesis about Language
Every amateur linguist has an opinion about the Wharf hypothesis, the idea that your language will affect your ability to think about certain things. Personally, I think it a bunch of crock. All languages are equally expressive, just some are more verbose at expressing the same thing. I think the language you speak has a grave impact on your brains ability to process phonemes (basic speach sounds) and grammatical patterns. For example, if you know the English tense system, the Russian one will seem awkward for a while and you may never be able to pronounce the Russian vowel bl correctly.
I think the idea that the language affects your ability to do physics, write computer programs, expound upon philosophy, is just rationalization for ethnocentrism.
Toki pona is the language of good talk and supposedly this will encourage happy thoughts. I seriously doubt this is possible, but it is a nice thought.