Researching various designs that have been implemented in RPG games, conveying important information such as health, stats, and other important details, is crucial to any gameplay. If the information is too obscure, the player won't understand when they are close to death (and should run far away) or will struggle to understand why their favorite magic trick just isn't going as well as it should. Similarly, if you make the UI too obtrusive, draw players' attention away too much, and obscure the real estate on the screen too much, then the result will be the same.
This balance is hard to maintain in any game, especially in RPG games, because we want to give as many capabilities as possible to our budding adventurer. It gets even harder once you start adding companions and hundreds of available skills and instant use items.