This came up in a much more complicated example but consider a case like this:
(defn simple 
(let [b (byte-array [(byte 0)])
m (byte 0)]
(= m (aget b 0))))
In the compiled bytecode, both m and (aget b 0) are known to be bytes, but both are boxed using Byte.valueOf(), then cast using RT.uncheckedLongCast() and finally compared as longs:
27: invokestatic #69 // Method java/lang/Byte.valueOf:(B)Ljava/lang/Byte;
30: checkcast #81 // class java/lang/Number
33: invokestatic #85 // Method clojure/lang/RT.uncheckedLongCast:(Ljava/lang/Object;)J
In a tight loop manipulating and matching against byte arrays, this boxing is significant for performance.
Attached is a test that demonstrates the performance difference between the byte(link: ) and long(link: ) performance to get an idea of the difference.