Well, we have to remember that the -aĵ suffix is also used in words like "manĝaĵo", where "manĝo" means a meal, while -aĵ is a thing. So basically, "meal thing".
This might be weird, but I think what the -aĵ suffix does is it makes things into a singular thing. Manĝo is an entire meal while manĝaĵo is just food. I guess this can also be seen with "porkaĵo" and "vestaĵo". Porko is a pig. So with aĵ it is pig substance, or pig. Vesto is a garment. With aĵ it's clothing. So my guess, although confusing, is that -aĵ basically makes something more specific. I'm not an esperantisto, but that sounds about right.
I also noticed while researching that aĵ turns some adjectives into a concrete thing or embodiement, for example bela (beautiful) + aĵ + o = beauty utila (useful) + aĵ + o = a concrete thing that is useful.
I also read that the word "aĵo" (thing), when used, is informal, even more than it is in English. So I think (take with a grain of salt, I am not an esperantisto, this is just a guess) that if you have something on the tip of your tongue, you'll want to use the suffix if you can. For example if you saw something beautiful, but don't know what it's called, instead of stuttering and saying "tiu bela aĵo..." you would instead say "tiu belaĵo..."
I would do some more research if needed. This link helps: https://lernu.net/en/gramatiko/sufiksoj
I hope I was able to help!