I like to think of the technique as a multi functional tool. You parry and trap your opponent's strike. Equally important, if not more so, while parrying and trapping you to cut an angle on your opponent to get into a safe position while leaving your opponent vulnerable. If karate is a fighting system of multiple distances, shuto mawashi uke is the technique that enables you to close the distance. Those familiar with Wing Chun, JKD, Silat will recognize what I'm talking about.
Kyokushin karateka who remember pinan sono ichi, might wonder about the different angled shuto mawashi uke at the end of the kata. No, they are not intended to allow you to meet additional opponents coming from different directions. They are meant to reinforce the idea of approaching your opponent form an angle instead of straight on.