When you complete quests or defeat various bosses you will receive sometimes gears which are better than what you currently have. I would suggest that you always equip the best equipment which you can because it is going to increase your power. You will see that if there is a piece of gear which is better than what you currently have, it will have a green arrow pointing upwards. This is super useful, as there will be some gears which will give you a huge boost in power (mainly some red gears which you will be able to pick up as drops from bosses). I suggest that you always equip the best gears possible because they will make a big impact on your character and they will help you get stronger.