Short verdict
Skip. Usually not worth luggage space, shipping cost, or the risk of buying before you know whether you need it.
Olive Young is convenient, but not every shelf is a good travel purchase.
What to know
Skip heavy shampoo bottles, generic cotton pads, products without clear ingredient comfort, and items that are cheaper from official stores at home.
What to avoid
Buy compact sets, Korea-only bundles, masks you will use soon, and products you can compare in person.
Final verdict: use Olive Young for discovery, not automatic bulk buying.