A hash object permits table lookup operations to be performed considerably faster than other available methods found in the SAS system. Unlike a DATA step merge or PROC SQL join where the SAS system repeatedly accesses the contents of a table stored on disk to perform table lookup operations, a hash object reads the contents of a data set into memory once allowing the SAS system to repeatedly access it, as necessary.
Thanks to Kirk Paul Lafler for this tip. Read more details in this paper from WUSS 2017: A Hands-on Introduction to SAS DATA Step Hash Programming Techniques.