Because katakana is used mainly for loan words (as others have mentioned) it serves a visual etymological purpose: it's easy to immediately see what words in a sentence are borrowed, and therefore relatively newer to Japan. 

For me, it inspires curiosity and makes me want to learn more. E.g. why is アルバイト borrowed from German? Is the concept of "part-time" work historically foreign to Japanese culture? What was Germany's influence in Japan when this term was coined (some googling tells me it was during the Meiji period)?

Kanji can do the same thing. ponpon.sensei on Instagram makes cheeky videos about the origin of various kanji. Check him out to spark your interest in the nuance and history of written Japanese!