When studying kanji with renshuu, I will sometimes get a kanji with a reading next to it. Then I have to select whether the reading is onyomi or kunyomi. Why is that important to know?
Those readings will help to read Japanese fluently, to comprehend and to converse with others. Sometimes, there are chances that there are homonyms (= words with same reading, but different meanings) and kanji help solve those potential misunderstandings. Mastering on- and kun- readings of Kanji characters make up a major part of Japanese learning.
On readings and kun readings are each more common to use in certain situations, so knowing whether a reading is on or kun will help you in guessing the readings of new words that use that kanji.
But if you don't want to answer those specific types of questions asking whether something is on/kun, you can just disable them in your schedule settings, under "advanced question types".
