- offload things you don't want
- put in useful stuff for yourself if you want to journey that area again later
- use as a temporary holdover if you find something really heavy and want to deliver it
- leave things for other players including deliveries
If you're running low on something you can see if any other player has left anything for you. Sometimes it's been a lifesaver for me.
Do it later! By the end of Chapter 2 (after you complete the Tiger Temple and maybe even secret area but before chapter end) Shingadang becomes a very easy (extremely easy) boss!