The CAT-ASVAB is an adaptive test which means the test adapts to the ability of the test-taker. It is possible to administer a shorter test this way than with the pencil and paper test. When you complete a subsection of the test, you can then move onto the next section of the test without having to wait for an administrator. Subsections are still timed however and on average it takes about 1 ½ hours to complete the computer ASVAB.
The ASVAB also known as the Armed Services Vocational Aptitude Battery is a test that measures your aptitude which is how well you do something.  A common mistake by most people is thinking that it is a measure of you IQ. Many people either forget this or don’t know this and they get worked up about the exam.  Saying that, it is also important to take a ASVAB sample test to insure you know what type of questions will be asked.    Another thing to keep in mind is every person in the armed forces has to take the exam and you are not being called out to take it. 
The various armed forces adopted all of those aspects in 1976. At that point in time, the test was in its written form rather than today’s more common form (computerized test format). The written form covers all of the previously mentioned areas as well, which is why both forms are still available. All-in-all that answers the question concerning the intention of the test.