>>48262348If you get a trip of the "table wind" (i.e. east) or your own direction's wind, it automatically gives you a yaku. You need at least one yaku + the rest of your hand "complete" to resolve the round. Rarer yaku are worth more, and the more of them you have the higher your combo.
One expensive hand can be worth much more than several cheap hands, but a quick cheap victory can be really good for edging ahead from second to first, or if you have a lead but are afraid someone else is closing in on a victory