I would say resin is one of the most critical aspects of the game because it helps you to level up your characters, weapons, and artifacts. With the help of resin, you can claim rewards from leylines, domains, bosses, and many more in-game entities. Now there are types of resins where condensed can be crafted and Transient can be bought. Though you can also get fragile resin from the battle pass, not everyone can purchase the battle pass. From my experience, I would say you should try to utilize your resin efficiently on the characters because it is a limited resource and cannot be replenished quickly in the game unless you plan to spend primogems. There's a limit to what a person can spend on this game, and if you don't come in that bracket, then it's easy for you to easily invest in your characters. But for, low-spenders or free-to-play players need to optimize their resin utilization and prioritize the characters they want to invest in in the long term.